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Basics of RAID
Doggie Fizzle writes "RAID has been common in business environments for ages, and is now becoming more viable and popular for personal computers. This article focuses on the the basics of RAID, and spells things out for beginners or tech veterans. From the article: 'The benefits of RAID over a single drive system far outweigh the extra consideration required during installation. Losing data once due to hard drive failure may be all that is required to convince anyone that RAID is right for them, but why wait until that happens.'"
Anyone ever get the feeling Zonk just doesn't get the Slashdot target demo?
We're NERDS. We created raid!
That's an awful lot of ads for a re-hash of well-known info. Are the editors sure this is frontpage worthy? It looks like a blatant attempt to get page views to me.
http://raid.com/
http://www.killsbugsdead.com/
There's an excellent guide to RAID levels (with pretty diagrams and such) at http://www.acnc.com/raid.html
A source of information with far better content, that isn't simply an excuse to sell ads.
Wikipedia
Depending on the your budget here in the UK you can get an 80Gb HDD for around £35, so split over some time you should be able to afford two (or an extra one if you already have one). This is a good enough reason for anyone to try RAID.
I myself currently have it setup to mirror my data across two 80Gb drives... Four months ago one of the hard disks died (funny buzzing sound, no access) but the manufacturers three year warranty was still valid, so I returned the drive to them for a free replacement. I received the replacement drive and shoved it in, mirrored the data back onto this new second drive and continued as before. If I hadn't have had this setup that data could have been permanently list. It also saves me from writing ten DVDs to store that much.
http://en.wikipedia.org/wiki/Redundant_array_of_in dependent_disks
Seriously, SATA hotswappable RAID 5, put an onboard controller on next gen motherboards, I dont care if its crappy compared to an expansion card, and you will have my money. Yeah we have RAID 0, 1 , 0+1, but no onboard commercial RAID 5 solution in mainstream motherboards. I know its more expenisve, but its also more efficient, and with every failed HD common users encounter the market gets bigger.
There is truth in humor.
RAID0 will increase your change of failure since you will loose all your data if a single drive fails. RAID0 isn't really redundant.
"now becoming more viable and popular for personal computers....Losing data once due to hard drive failure may be all that is required to convince anyone that RAID is right for them"
I was thinking they were referring to "Joe Bob Home User" who is starting to use RAIDS more, which is true but, as far as I have seen they are NOT using it for RAID1 - (Mirroring and Duplexing) they ARE using it for RAID 0 (Striping) so their system apps/games run faster.
Ave Molech Setting
Here is a link that explains the basics of computer hardware; I think that it's a good companion piece to the RAID article: http://www.angelfire.com/rings/judy_patch/
Okay I guess it appeals to geeks and fancy computer modders and all. But really, when it comes down to it, a decent main hard-disk, a tray in the second bay for backup hard-disks, and a reasonable backup regimen that people keep up is all a "personal" computer user needs.
Personally, I have 3 backup hard-disks, one that keeps a "clean" base system that I update every 6 months or so, and 2 that I do full differential backups on every 3 days. The "clean" hard-disk is kept off-site, and a script tells me when to do the backups on the other 2. And for very very important files, I just write them on a CD on the spot.
With that, I've yet to lose a single file since I started using Linux in 93 or 94. My solution is cheap and doesn't involve fancy raiding. And I'm quite sure I overdo it, most people could do just fine with one main hard-disk, one backup hard-disk and a little discipline.
"A door is what a dog is perpetually on the wrong side of" - Ogden Nash
With RAID, you still have a single point of failure. Instead of it being your hard drive, it is now your RAID controller. So what is the advantage?
Since a RAID controller doesn't have moving parts, is it less likely than a hard drive to fail?
Don't forget that Friday is Hawaiian shirt day.
. Losing data once due to hard drive failure may be all that is required to convince anyone that RAID is right for them, but why wait until that happens.
:)
Because otherwise, you can tell them all about the wonders of RAID and all they'll do is just pretend to be interested while secreting thinking that you are some mad geek.
Tell them about the wonders of RAID after they've been kicked in the nuts by a drive failure, and you sure as hell would be getting their whole undivided attention.
Making the most of your effort man.. that's what it is
Online backup with Mozy, sounds like Ozzie, but more!
Cuz the boss won't cough up the money until it happens.
RAID: Redundant Array of Independant (Inexpensive) Disks
Why? If one disk dies you don't lose your data.
RAID 0: better performance, worse reliability
RAID 1: mirroring; no performance benefit
RAID 5: striping w/ parity; perfomance benefit + reliability
How? With Linux of course!!! 50f7w4r3 R41D is teh r0x3r
Really guys, is this article really necessary? There's enough about RAID in basic CompTIA A+. I don't really think this needs to be posted on the front page. But what do I know; I'm just an AC.
As a (poor) student, I find that I simply can't afford an extra hard drive! I got a 2nd hand DVD burner from a friend for £15 and backup all my really important stuff (Code for university, photos, etc) every week. All my MP3s go on another DVD along with the hard disk, and they're "backed up" on my MP3 player anyway.
As of yet I've never had a single hard disk failure... but I've not really got anything I'm bothered about losing, so RAID isn't worth it for me.
There is nothing more practical than a good abstract theory.
IDE HDD Talking to IDE Controller:
HDD: I'm gonna need more time for that write
Contr: Yeah OK, go ahead good buddy
Contr: What's up?
Contr: What's up?
Contr: Error: Drive controller timeout error
SCSI HDD Talking to SCSI Controller:
HDD: I'm gonna need more time for that write because I found a bad block
Contr: Yeah OK, go ahead and remap that bad boy
Contr: What's Up?
HDD: Need more time to map that bad block
Contr: Yeah OK, go ahead
HDD: All done, grabbing the next command in the queue
Personally, I prefer daily backups to another HDD (use rsync, it's great), that way, if I make a major *oops* during the day I know I have a very recent backup immediately available, this is something that RAID cannot protect you from (the human failure).
s / is a great page to learn about using rsync to make easy backups.
If then I've still got money to spare, I'll look at mirroring.
http://www.mikerubel.org/computers/rsync_snapshot
Anyone else notice the error in the RAID 5 explanation?
Kneel before Sig!
Yes!!!! I now can point my PHB to this article, and then to the article on how to turn IPods into a raid, and that should be enough to convince him to buy a few dozen. Now I will just need to explain to him why having a spare Ipod stored at my house will be a wise decision, you know, just in case the vendor closes it doors tomorrow or does something 'crazy' like switch architectures next year.
There are two types of people: Those that have lost data, and those that will.
Don't forget, though kids - RAID won't protect you from deleting your own data, or a malformed script trashing stuff.
Get your own free personal location tracker
... eh Raiders.
Seriously, can't we learn about how hot a redhead is in bed vs a blonde?
"Losing data once due to hard drive failure may be all that is required to convince anyone that RAID is right for them, but why wait until that happens."
Why? That's actually quite simple. Losing consciousness once due to a brick falling on the head may be all that is required to convince anyone that a helmet is right for them, but we don't see people wearing helmets, do we? Do people wear bulletproof vests? No? Why not? After all the benefits of a bulletproof vest over an ordinary vest far outweigh the extra consideration required during installation! Please, people, could we stop being such naive children thinking that our beloved industry is somehow special, that ones and zeroes have more value than humen lives? Could we please stop being so pathetic once in our lives? RAID may be a nice idea for "nerds that matter" but it is not for grandma. Period.
Karma: Positive (probably because of superiour intellect)
... but how often do personal backups actually happen? I'm one of those guys that has been taking home backups seriously for a long time, and has a collection of obsolete tape units to prove it. And backups still do not happen often enough if it requires me handling tape.
Let's face it, discipline is a drag, that is why at work IT people are paid to schlepp around stacks of locked cases full of back up tapes to be shipped off site.
So... for my home file server, I went to RAID mirroring, with a 3rd drive in a drawer. A mount-copy-umount chron job copies to the drawer-drive. Drawer-drive gets swapped and taken off site "when I think of it". Because... RAID only protects you from falling over hard drives. It does not proctect you from:
1) Ooops, I wish I hadn't deleted that.
2) Gack! My house just burned down! And took 10 years of tax data with it!
3) Power supply goes wonky, causing both drives to scribble random scorfulentness everywhere.
A home RAID system does not need to be expensive. Who needs hot swap? Use cheapo PATA drives. A few hours of down time for the wife and kids is OK. It doesn't take a big, bad CPU, and software RAID works great.
from your mouth to Steve Jobs ears. If anyone will ever make RAID 5 a desktop standard its Apple. Its just too bad the G5 tower only has room for 2 drives. I'd take three 120GB drives in a Raid 5 array over a 300GB drive any day. People need speed and reliability much more than storage these days with the smallest drive you can get most places being 80GB.
Choose your Raid Click on which type of raid you want to know about, and it tells you what its good for, disadvantages and advantages.
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I've reported this in their forum. Hopefully somebody will fix it (or at least take the advice under consideration).
Im thinking of adding a couple big disks to raid together for user files
:D
And keep my small hard drive for the operating system, if OS dies Id like to restore its image from the raid array.
Am I dreaming here? or how can I do it?
For those who have run out of internal space in their boxes, and who don't have external SATA or expensive hardware boxes, you can run RAID over Firewire.
.
The problem, however, is that out of the box Windows refuses to "promote" an external disk to dynamic, which is required on all post-NT4 rigs for RAID.
The solution is to add a semi-documented Registry flag, EnableDynamicConversionFor1394
HOW TO: Convert an IEEE 1394 Disk Drive to a Dynamic Disk Drive in Windows XP
Couple that with a cheap 4-bay firewire JBOD box and any spare old enclosures and you are set!
I run 2TB in various RAID configs on my Windows server (main and near-line storage). Have done so since 2002. No problems with the external boxes. The support for external firewire RAID is a little gnarly in Windows 2000 - volume must be mounted as a named virtual directory and cannot be mounted as a letter drive. Later Windows give you both options.
Da Blog
With hardware cost falling steeply, when will it become viable for home users to start having RAID-based PCs?
All said and done, many of us do keep fairly important data on our home PCs. How many of us make an effort to back it up?
Warm regards,
Sharad Agarwal
AlcoHaul: We lift spirits!
RE:"Losing data once due to hard drive failure may be all that is required to convince anyone that RAID is right for them, but why wait until that happens."
data backup is what CD Burners are for, well they are plenty good enough for me.
When you're setting up a RAID set using both striping and mirroring, do you want to set up two stripes and then mirror between the stripes (0+1), or do you want to set up mirrored pairs and then stripe those mirrored pairs (1+0)?
This is a quiz, and your data will grade you.
What you want, by far, is RAID 10 (1+0).
When you set up two stripes and then mirror across them, if you lose two disks, any disk in the first stripe and any disk in the second stripe, you lose all the data.
If you stripe across mirrored pairs, then the only way to lose data is to lose both drives in one of the mirrored pairs. You can lose any other disk than the second drive in a pair, or even many more disks, as long as they aren't both in the same mirrored pairs.
This doesn't make a difference with 4 drives. At 6 drives and up, use 10. Your data and users will thank you for it.
We need something other than harddrives. They are the slowest part of computers and they crash.
A laser/magneto drive would be more reliable and have more density ?
I am running RAID 5 on my desktop server right here. It has a P4 3 year old Gigabyte motherboard. It's not hotswappable because it's not enterprise level (and I don't plan on having to hotswap all of the time, only when shit happens) but it gives me the RAID 5 that I like to use as a backup using software based RAID on Ubuntu Linux. After the install, it it would be just as easy for Grandma to use as if it were not RAIDed and I am certain any /.er could figure out the install for most any Linux distro.
Can I have your money now?
I'm planning a 800 GB (4x400GB) RAID 10 array whenever I come up with $1200. Now, I'm a total RAID newb, but even after raiding that articlem I still didn't learn anything. I'll take the Wikipedia article any day.
Our most critical stuff is mirrored on seperate disks that are on seperate backplanes attached to seperate controllers. So the only single point of failure is the system, and if it goes down well the data isn't that useful anyhow.
Also yes, RAID controllers are much less likely to fail. For the most part, if a solid-state device works for the first 30 days, it'll work forever if it's taken care of. There are exceptions, of course, but lacking any moving parts there just aren't a lot of ways for them to wear out, particularly for things that don't generate much heat and thus son't have much thermal expansion/contraction.
With disks it not a question of if, but when they'll fail. Eventually, something will wear out and they'll stop working. Might be 20 years, but it'll happen.
Unfortunately I don't have any empirical data so I'll just relate personal experience, even though it's not a proof: We see probably 10-20 harddrives fail per year for all our systems. Not unreasonable, we have a lot of systems. We see less than 1 harddrive controller fail per year. It almost never happens.
I had my system hard drive fail fatally on me, emails and so forth, only some random backups elsewhere. Right then and there I decided that no more will a hdd failure steal my stuff from me and bought 4x120gb drives (size/price ratio at time was optimum) and a Promise controller. Now I got ca. 240gb RAID 01 setup, mirroring gives reduncancy and striping keeps the array at least as fast as those drives used separately.
One hdd did fail on that array, and I just replaced it with warranty replacement hdd. No hassle, just carefree usage.
The piece of mind is worth LOT more than those extra drives. I DO NOT like the menial job of building the OS from zero to working state, just because of a hardware failure, WHEN I can just as well avoid it.
Proability of a failure greater than zero (0) is not zero. And I like it to be zero.
-Is the meaning of life vanity, or is vanity the meaning of life?
A lot of motherboards come equipped with RAID capabilities even if the end user doesn't know what the acromym means.
Now that external USB/Firewire drives have become more affordable as a backup solution, I recommend that. Confession: I don't know WTF I am talking about.
At one time, I thought RAID was teriffic. But honestly, I think it's way over-rated and exists primarily for the benefits of systems builders and manufacturers to sell people additional hardware and increase their profits.
1. RAID implementations on most consumer-grade motherboards (EIDE RAID with Promise controllers on-board, and so on) are cheezy. I've tried using them for several years now, and I ran into lots of unexplainable "glitches" that never occured when I took RAID out of the equation. (EG. The RAID array would suddenly report a failed drive, yet when I'd pull the drive out and try reformatting/reusing it on another machine as a stand-alone C: drive, it would have no problems at all and S.M.A.R.T. reported it was fine too.)
2. As others pointed out, the RAID controller is the new "single point of failure" - and amazingly, they do seem to go bad far more often than I'd expect for an expansion card on "better quality" RAID setups. I used to work for a place that slowly had every last one of their Dell "PERC II" RAID controllers die off, one by one, on their Poweredge servers - causing all kinds of hassle. (The card was no longer in production so finding identical matches for all the dead ones wasn't so quick or easy.)
3. If you buy both of your drives at the same time, from the same place, they likely came from the same production run - so if one drive gives out, there's quite a good chance your other one(s) in your array will follow within a short period of time. After all, both have been running for the exact same number of hours of operation, at identical temperatures inside the system. More than once, I've seen a drive fail in a mirrored set, and then the spare died before the user got a chance to swap out the first one. So much for the data....
4. If you actually get "hot swap" drive trays for your RAID system on a home-built PC, good luck with those too. Most of the ones I've purchased locally or over the net have been poor quality - creating yet another "point of failure". The cheap, little cooling fans in them usually wear out quickly, and I've had the little circuit/switch break on a couple that lets you put the key in and turn it to power the drive on/off to prepare it for removal/re-insertion.
Honestly, I think the only solution is a good backup to off-site media if you have really important data to keep. For many home users, this probably isn't even a huge deal. Throw your resume and important documents on a flash drive or CD-R/DvD-R disc, and if the rest ever crashes - it's a good excuse to do a fresh, clean OS re-install anyway.
With Blu-Ray and HD-DVD on the horizon, each offering 30-50 GB per disc and in some cases more at a fraction of the cost, why would a normal consumer need to backup stuff using a RAID array? You're going to need to replace the broken hard drive anyway. I can see RAID being useful for businesses where they want as little downtime as possible, but is there really any point in buying more hard drives when you can get the same effect with DVDs or the upcoming BluRay and HD-DVDs? You can cite performance as an advantage using RAID 0, but as has been shown, there really isn't any.
It's amazing how common RAID is now, especially (S)ATA RAID.
In video editing, RAID is everything. External SATA RAID is the big thing now, and it works pretty well, even when it's OS based. What I haven't seen yet are (relatively) cheap SATA RAID 5 enclosures. That would be the Holy Grail of fast media storage.
Adblock must be doing it's job.
The man who trades freedom for security does not deserve nor will he ever receive either. - Benjamin Franklin
I've sold Entreprise hardware / software / projects for over 13 years, and the handful of catastrophic data losses / service interruption / nightmarish server setup / stability issues my clients have had have ALWAYS been with RAID systems.
;-) I have no real-life experience with FC and the thing over ethernet yet. i'm VERY leery of my customers being used as beta-testers / guinea pigs.
...
Of course, if you're using RAID it's because you need capacity / speed / reliability, and while it seems the first two are indeed delivered, there is a HUGE reliability issue.
Back in the days when i was selling Dell's own RAID array (can't remember the name), it was well known at Dell that the controller software was buggy, they fired the programmer but still sold the stuff. And thing haven't improved since. A couple of years ago it took a Compaq high-end VAR several MONTHS to get multi-gig RAID5 setup working. My brother works for a very large company, and after months of problems, their SUN lead person admitted that SUN has issues with their RAID controllers, especiallly the replacement ones / spare parts. Remember when SETI@HOME went down for a week a couple of years ago ? SUN RAID controler problems !
My advice to clients is to avoid RAID whenever possible. Have spare servers, do very frequent backups, split your databases, have gobs of RAM... For the cost of a first-tier RAID system, you can buy a lot of other stuff, that WILL be useful in a lot more cases: fried servers, corrupted files... It's too bad the SCSI disks we use lag so much is capacity compared to ATA. I haven't done any SATA yet.
The one thing less reliable than RAID is clusters, BUT i haven't handled clusters in a while, i'm talking 5 years ago. May be the new Linux ones are better
My 10 cents
Sorry for the "AC", but since I'm naming names
- What happens when, say, an IDE drive fails using software raid on linux? Does the machine stay alive, or do you need to remove the drive and reboot to get back to working?
- How about failures with full hardware raid, like an LSI megaraid card. I've unplugged a drive with one of these and it beeps a lot, and seems to recover when they get plugged back in, but what about a true drive failure?
- I'm also really curious about these new SATA raid controllers that libata calls "fake" raid controllers. Can they gracefully handle a disk crapping out?
TIA to anyone who's seen enough failures to comment on this.As a future project, I was thinking of building a RAID 5 solution from stock parts, but then I came across this
2 6
http://www.lacie.com/products/product.htm?pid=103
Which seems not to be much more expensive than building your own. The same company has a nice line of other desktop and network drives (I have no connection to this company whatsoever).
Drawbacks?
Imposing Libertarian views on everyone online since 1992.
Seriously is this site about news or info you can find in books 15 years old?
Don't use stripping for performance unless you do video editing:1 01&p=10
http://www.anandtech.com/storage/showdoc.aspx?i=2
Don't use RAID0 for redundancy because its not worth the effort, you still have a single point failure of the raid controller card. Stick with a 2nd device (usb drives are good) which you simply copy your important data to every week or so.
Unless you can afford and need RAID5 (5 hard drives) forget about RAID and be happy your not wasting your time with it.
I worked for years in development of RAID solutions for a major manufacturer. One of the problems with selling RAID solutions is the lack of understanding, or the prejudice and bias of the people who were supposed to be specifying and buying the hardware.
The 'tutorial' of the parent article is talking in kindergarden terms, oversimplifications and obsolete term, and overlooking some of the issues with using RAID. It's a good example of the true lack of understanding about the subject. By now, there are so many types of solutions that the term RAID hardly applies. But, even 10 years ago companies like Compaq had innovative rudundant storage solutions that were enterprise ready.
Best regards.
My favourite failure was having the array accelerator memory fail (192mb)while I was working on a 2003 server. Unfortunately I was making changes to active directory at the time - and some of the drive writes happened to be in the array memory at the time.....ah bugger....
"If anyone will ever make RAID 5 a desktop standard its Apple. Its just too bad the G5 tower only has room for 2 drives."
Now THAT is the most hilarious thing sentence I've read in a long time.
Sometimes my arms bend back.
I just built my first RAID server. I've been the victim of 2 hard drive crashes where I lost data. I have a large media collection that includes family videos of over 30 DV tapes I've captured. Between all the media as well as other critical info I finally decided to dive in. Since basically all I needed was a file server that also offered redundancy I opted for RAID 5. I didn't need huge performance and in a RAID 5 configuration you only have to sacrifice 1 hard drive for redundancy as opposed sacrificing equal numbers for mirroring. This seemed like a good comrpomise to me. After making that decision I had to find a controller. I ended up going with a Promise Technologies SATA raid card. I mainly chose it due to the affordability and good reviews. Be careful of some cheaper cards that only offer RAID 5 in software. Another major consideration was the fact that I only had a standard PCI slot available in the Dell 400SC server I was using. That limited my choices quite a bit since most of the other contenders only worked on a PCI-X bus which requires a much pricier server motherboard. So my build went smooth and I am extremely happy with what I now have. Here's another good bit of advice that a friend passed on. Make sure to test your array after you are done by forcing a failure to understand how your hardware / software deals with it and you are aware of what to expect. I did this by starting to copy a 4GB file to the array and during the copy I unplugged the SATA cable from a drive. The software quickly alerted me of the failure. Shortly after I plugged the SATA cable back in and rebooted. The RAID bios also identified the failure. I then booted into Windows, launched the RAID utility and watched as it rebuilt the array. Everything went smooth and I now feel very confident about my server.
More ads than pages and the content sucks to boot. Why is this wad allowed to post this?
What I don't understand is why this made it to the frontpage, seriously how many people on slashdot don't know what a RAID is? I've known what RAID is since I was 13. What kind of crap passes for a submission nowaday anyways?
If you pay your taxes you support terrorism!
I'm assuming all your "enterprise" RAID setups were IDE. RAID with a good card, and SCSI drives does excellent.
The one issue I think every HD user should be more worried about is HD temperature. More drives fail due to excessive temperature than any other reason. RAID really isn't going to help if all the drives are running in an excessively hot environment.
---
The "are you a script" word for today is selfish.
Raid 5 can be configured with a minimum of three drives.
Interested in RAID? Google, or check out: Storage Review's excellent information.
And for god's sake try not to get yoursefl stung.
You don't really nead a whole article about using RAID.
A guy walks into a bar... well, I forgot the joke, but the punchline is that he's an alcoholic.
I have always used RAID M you have more then one HD in your system and you copy what ever is important to more then one drive. Since I use a Mac i also have the OS on other drives so if my OS gets toated I just boot from a different drive. Works for me for the last 10 years.
http://Lenny.com
a groundbreaking article describing how humans breathe air by breathing in and breathing out.
www.this-is-not-news.com
that zonk is a fucking retard. =]
You don't need backups if you don't do anything important. I should know. I am an official member of RAID - Redundant Army of Independent Derelicts. Of course, before PC (political correctness), back in my day, we just called ourselves HOBOS. (Huge Obnoxious BO Smellers). One day, I was wetting myself and talking to God, and he said, "Jed, get away from there, you don't need no RAID. Black gold, Texas tea.", Next thing you know, I'm a Lotto (TM) millionaire. So, I went to California and started a dot-com company. That didn't work out, but I don't miss it. Nothing has changed for me. To RAID or not to RAID, that is the question, I ask myself every time that wiener dog goes by... [Can you beleive they give 5 whole mod points to people who use public access terminals!]
This issue is a bit more complicated than you think.
1. RAID implementations on most consumer-grade motherboards (EIDE RAID with Promise controllers on-board, and so on) are cheezy. I've tried using them for several years now, and I ran into lots of unexplainable "glitches" that never occured when I took RAID out of the equation. (EG. The RAID array would suddenly report a failed drive, yet when I'd pull the drive out and try reformatting/reusing it on another machine as a stand-alone C: drive, it would have no problems at all and S.M.A.R.T. reported it was fine too.)
Yes. Promise controllers suck. I have one and occasionally it "forgets" how the drives were set up. Nothing is actually wrong with the drives. It is possible (on mine anyway) to re-enter the configuration and resume normal operation without data loss. The trick being is answering NO when asked if you want to quick initialize the RAID.
I've had no problems with my other on-board RAID controller (made by VIA).
I want this account deleted.
If you buy junk, expect it to fail-- and that means anything sold by Dell to start with.
1) RAID controllers-- real ones-- are highly reliable. Yes, a power supply surge can kill anything. Yes, backups are a good idea. But if you're in production, backups are stupid; high-availability clustering is important. Client/users that need RAID get a benefit.
2) See the comment about using Dell products; they make nothing themselves, and therefore are the WalMart of computer quality-- driving OEM costs to the bone, and therefore, often quality, too.
3) There's no research or logic that supports this. It's another computer urban myth.
4) Once again, buying from the bottom of the barrel is an unwise posture for a serious professional. This isn't ToolTime.
Backups are a good idea, They work when data can actually be restored in under a century. It's nice also to have mirrored external USB 2.X or FireWire/IEEE1394 drives, too. But a majority of people don't even do that. In production environments, you're destined to do it and for all the right reasons. But it's not a good excuse to re-install an OS. You do that only with Windows. A real OS can live a long healthy life.
---- Teach Peace. It's Cheaper Than War.
Has anyone tried using Linux Software RAID and a bunch of external USB drives? I'm wondering what the performance would be like for a light-duty file server. I want to go from a huge case to much smaller case, and that means getting the RAID drives out of the case.
I was looking through some raid articles and found this.
... sorry, had to throw in the corny bug joke.
http://www.ofb.net/~jheiss/raid10/
It explains how 1+0 is better than 0+1 either way..ROACHES HATE RAID!!
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As far as desktops are concerned - well, RAID and cheap just don't mix. For instance, if you just want reliability, RAID 1 is enogh (2 drives). If you want reliability + fast writes, you need RAID 1+0, which means 4 drives (RAID 5 only gives faster reads). Furthermore, a good controller is crucial (from my experience, these generally cost upwards of 100$).
Finally, RAID does not subsume in any way a good backup system. I've seen cases where a damaged controller broke both harddrives in a RAID 1. However, for (most) desktop PCs, a good backup system does subsume RAID, since it's generally easy to just use a different computer, and get all the files from the backup.
For me, the excellent piece of software backuppc running on a cheap box (~300$) has worked like a charm. This might not look cheaper than RAID, but considering that I'm using just one box to back up 10 other machines, it's pretty good.
The Raven
No, it's not "Real-Time" but it suits our needs in our home office situation.
I use "Smart Synch" software to incrementally copy the desired directories from the working computers to a "Backup server", an older Celeron machine on the network. Separate partitions are set up for each computer that is being backed up. At Midnight the incremental backups are made.
Then at 2:00 a.m., Smart Synch running on the backup server makes another backup to a USB hard drive plugged into it. That USB HD is on a regular plug-in timer so that it only runs during the time of night when a backup to it is being done. The idea there is that the running time is limited and drive life is extended. Weekly, a backup DVD is burned and stored off site. Am I being anal? Maybe.
"Do the Right Thing. It will gratify some people and astound the rest." - Mark Twain
Ultimately, what it comes down to is that mirroring merely makes the hardware more reliable, it is not a backup technique.
It can be part of this nutritious breakfast^W^W backup technique:
0) shut down the box
1) swap a fresh/new/wiped drive for one of the mirrored drives
2) rebuild the RAID
3) store the just-pulled drive appropriately (e.g. off-site) along with a second identical RAID controller
Now if the machine goes completely belly-up (as in a fire) the user can install the secondary RAID controller and the data-laden drive in a fresh machine, add another fresh/new/wiped drive, and rebuild the RAID in the new machine. This may not be terribly convenient nor perfect for everyone but it will be effective.
Remember, kids: just because a particular technique doesn't perform a task all by itself (in this case RAID 1 != backup) that doesn't mean it can't be part of a larger picture.
I want to drag this out as long as possible. Bring me my protractor.
I mean if you just want fault tolerance then use straight up mirroring. If it's for currency then perhaps you need a journalling file system with checkpoint rollback/rollforward.
My father has trusted his data (against my advice) to fakeraid chipsets on his various motherboards twice. He just got done *losing* all of his data for the second time.
Best we can tell, he had one drive go without his RAID controller warning him; then had a second drive go, killing the array. He spent weeks with a dead PC playing with all kinds of special Windows bootloaders and disk recovery tools trying to get his files back.
Fakeraid sucks because it's just a line item on the sale of a modern motherboard. The inclusion of the "RAID" functionality is borderline fradulent. REAL RAID controllers, of course, have a coprocessor and often battery backup and leave all of the storage details to themselves rather than some fly-by-night driver in the operating system.
It's no surprise that they come with virtually nothing in terms of recovery software.
The happy median, I've discovered, is Linux md. md supports many RAID levels, and according to some benchmarks will certainly outrun fakeraid in performance (which doesn't particularly surprise me). The administration tools let you simulate drive failure, monitor array health, create degraded arrays, and the documentation tells you what to do when something goes wrong.
I also disagree with the story. People always confuse RAID with backups.
RAID provides *redundancy and availability*. If a disk fails, you can get your system up and running again almost instantly - obviously very important in the business world.
Backups provide *data protection*, so that if your data is lost or corrupted for any reason, you can retrieve it from a safe copy.
The only purpose I can see in the home for RAID would be RAID-0 (striping) for performance improvements. But the only home application I can think of that would utilise that improved sequential throughput would be video capturing/conversion. Most home applications are random I/O intensive, which doesn't get much improvement from striped disks.
For backups at home, most people should be able to get by with occasionally burning a CD or DVD of their really important documents and records and storing that at another location. If people *really* feel they need a backup of those "linux distributions and home movies" that are occupying hundreds of GB on their hard drives, external USB hard drives are probably the best option at the moment.
Serving Suggestion: Defrost
Raid 10 needs 4 drives but a much less expensive controler. Adequate performance for Raid5 means a hardware XOR engine. Such a controler starts at about $150. A 4th 200GB drive is available for less than $100.
RAID 10 is both faster and more reliable than RAID 5. (Though the chance on losing data for either is mighty low)
RAID5 really only makes sense for arrays built out of the largest disks available.
Losing data once due to hard drive failure may be all that is required to convince anyone that RAID is right for them, but why wait until that happens.'"
Isn't it human nature (or at least that's what it seems) to wait until something "bad" happens?
That goes for obese people, smokers and yes even computer geeks.
Why eat all the fat? I'll just burn em all!
- Wait til your 40-50 and check that cholesterol strike...
So many people smoke and get away with it so I will to right?
- Yeah wait til you get some health problem that will make you say "OH NOES!"
Why I need firefox? ActiveX hasn't screwed me.
- A week later "omfg whats all this junk, I want Firefox!"
Why Do I need RAID or even a burner? I got 3 hard drives that contains all my data!
- 8 months later, 1 hdd crashes "AH F*K ALL MY Pr0n!" and then he thinks of having a simple RAID 1 setup...
We always wait because we are lazy and cheap.
I wonder if I'm the only person to file a FireFox bug report that the "Read More" link to this article on the front page kills the new version of FireFox? For some reason, this URL aborts FireFox 1.0.6:
/ 22/2159230&tid=198&tid=1&tid=218
http://hardware.slashdot.org/article.pl?sid=05/07
Oddly enough, the link works fine if you copy/paste it into FireFox's address box, but not if it's clicked on from the main SlashDot page. Can anyone confirm this?
9/11 Eyewitnesses to Explosive WTC Demolition 1 of 2
I had high hopes for nvidia's nforce4 onboard RAID, but after someone said it sucks, I don't know what to look for. Are those $100 Promise cards good game?
This article focuses on the the basics of RAID...
The the the the editors must be be be be blind. How long ago did you give up giving even the most cursory inspection to the summaries? I know you all think it's only the headlines that matter, but some of us (i.e., all of us) readers wish you would do a little more, you know, editing.
"Adequate performance for Raid5 means a hardware XOR engine. Such a controler starts at about $150."
I must be the only one who knows how to shop for computer gear.
1. The average user does not need RAID.
2. The enthusiast does not need RAID.
3. RAID is not a replacement for backing up.
RAID is only good for two things: To protect against a hard drive failure when an uptime as close as possible to 100% is required; and to increase performance in the form of data throughput.
Alright, let's cover them one at a time. The average user (anyone who just buys a Dell to surf the web,) doesn't need RAID. Hard drive failures are fairly uncommon. And the to the 'average' user, 100% uptime isn't anywhere near a necessity. Also, data throughput isn't that important, either. (Besides, for most people, buying a faster hard drive is both technically better and more cost effective.)
Most enthusiasts (gamers, hardware tweakers, modders, etc,) don't need RAID. Again, hard drive failures are fairly uncommon, and your average enthusiast doesn't exactly store cures to cancer or rocket science on their drives. (No, the old MS Space Simulator doesn't count as rocket science.) Besides, most enthusiasts use RAID-0, which isn't really redundant. Which brings us to point B. The only thing RAID-0 measurably improves is sequential STR speed (Spindle-to-RAM, the speed of data going from the platter to the drive's internal cache.) And there are very few enthusiast tasks that do better from a raw higher throughput. (Even capturing video doesn't matter, as the slowest hard drive today can easily keep up with uncompressed HD!) Oooh, so your Doom3 level loads 1/2 a second faster. In single-player mode, it doesn't matter at all, and in multiplayer, the server waits for everyone to load anyway. RAID doesn't help for random seeks. A faster spindle helps for that. A better drive caching algorithm and a larger drive cache helps for that. If you have a 40GB, 5400RPM, 2MB cache drive, you'll see a tremendous improvement by going to a Raptor, or to a 15k RPM SCSI drive. You will see very negligible benefit by getting a second 40GB, 5400RPM, 2MB cache drive and putting them in a RAID-0.
Finally, the assertion that RAID prevents data loss. The only data loss it prevents is loss due to a failed hard drive. It doesn't protect against user error, viruses, or physical damage that destroys the whole computer. If your data is truly vital, you need to be backing up, even if you do use a RAID. Yes, businesses with vital information who need (as close as possible to) 100% uptime need RAID. That's it. Even then they still need backups.
Another non-functioning site was "uncertainty.microsoft.com."
The purpose of that site was not known.
...I like this guide better.
Yes, it's a little old. But, I found it to be very comprehensive, especially for its day (remember, RAID 0 and RAID 1 were only beginning to show its face in the consumer market when the guide was written). It's actually a mirror of another page, but since I stumbled upon this one first, I don't remember where the original is or what it might have been called, or, for that matter, which pages/paragraphs were in the original and which ones were not.
"If a nation expects to be ignorant and free in a state of civilization, it expects what never was and never will be."
One glaring error:
RAID can be run on any modern operating system provided that the appropriate drivers are available from the RAID controller's manufacturer. A computer with the operating system and all of the software already installed on one drive can be easily be cloned to another single drive by using software like Norton Ghost. But it is not as easy when going to RAID, as a user who wants to have their existing system with a single bootable hard drive upgraded to RAID must start from the beginning. This implies that the operating system and all software needs to be re-installed from scratch, and all key data must be backed up to be restored on the new RAID array.
Again, wrong, wrong, wrong. There are hardware RAID 1 controllers that require no drivers and you don't have to do squat - just power down the server, install the RAID 1 on your IDE interface, plug in the new drive, hit the power, and away you go. The controller is smart enough to automatically sync up the two drives in the background.
-- Ed Carp, N7EKG erc@pobox.com PGP KeyID: 0x0BD32C9B What I'm up to: http://intuitives.mine.nu
In my neighborhood, yes they do! ;-)
9/11 Eyewitnesses to Explosive WTC Demolition 1 of 2
The other problem is that most people who work at Slashdot have very limited skills outside of the core competencies it takes to run a web forum so we tend to get uninformed blather and the publishing of stories that even simpletons with science degree would not publish.
An Education is the Font of All Liberty
In the article a few things are omitted that would be important to note if you were building your own array.
1) The article notes raid 0+1. Raid 0+1 is VERY dangerous. You want 1+0 not 0+1. The main reason is loss of any disk from a 0+1 will immediately degrade your array. Also keep in mind vendors call this 1/0, 1+0, and 10. Also keep in mind vendors LIE about 1+0 vs 0+1
2) The alternative to 1+0 is raid 5. Raid 5 had some significant drawbacks to its use. These are read-modify-write and the calculation of checksums. In fact, unless you get higher end raid controllers, it is incredibly slow. Software raid 5 is even worse. So be careful here too.
Since none of this is new groundbreaking material by all means go look up whatever storage solution you decide on implementing. Learn how each solution works and your normal utilization.
Raid is big storage for cheap - especially SATA Raid. A hardware card can be had for under 300 bucks for a 6 unit LSI. For a neat experiment, try Linux software raid booted from a Knoppix 3.9 CD. On a regular IDE subsystem, you can have your raid 5 which is independant of the os layer. The big concern is backing up that big 3 drive, 320G raid device once you fill it up. Especially if your a corp and you want to level 0 all the invested time/money that is laying on that device. It can get quite pricey, and Amanda will not span a level 0 to multiple tapes.
Join the Slashcott! Feb 10 thru Feb 17!
a decent case is a much better option...
That's a pretty nice case, but firstly it's not available yet, secondly it's a PC case, awaiting a motherboard, power supply, RAM, and so on, and thirdly, a cheap firewire 4-bay JOB enclosure costs around $70, all in, power and fans, and you're good to go.
The annual power consumption difference between running an enclosure or rack of disks and a whole intelligent CPU storage node is substantial: on the order of ~$100 annually. Not to mention it's also more of a PITA to support, with many more parts liable to failure or corruption. When I want to complexify my life by setting up intelligent nodes, rather than just slaving drive boxes, I usually go with a good Antec fileserver case.
Da Blog
Consider:
RAID 10 disadvantage: "All drives must move in parallel to proper track lowering sustained performance". In fact each drive can seek independently for reads and only pairs must seek together for writes.
RAID 1 advantage: "Transfer rate per block is equal to that of a single disk"
RAID 5 disadvantage: "Individual block data transfer rate same as single disk"
Would be nice if it was consistent about whether that's good or bad.
RAID5: "Highest Read data transaction rate" except for RAID 10, of course, where you've less chance of being bottlenecked because there are two sources for each stripe.
RAID5: "Medium Write data transaction rate", only the lowest of all except 50, because of the parity calculating and writing to a second drive.
I have installed software RAID 1 (mirroring) on a system with two SATA drives 2.6 kernel. It was easy with the new debian installer in Sarge.
The speed increase of the system was wonderful. Boot times, responce times etc. Write times remain the same but read times are halved.
I have since upgraded all our Linux servers to PATA Raid1 - Requires no raid controller. Query times have dropped. All for the price of a few 40GB IDE drives.
I now want RAID 1 for my home machine.
For the boot times etc not just data redundancy.
Don't make your problems my problems!
I have installed software RAID 1 on my Linux systems
and they boot faster. No hardwaer required, uses linux kernel software RAID - much faster than hardware raid on a dual processor system.
Works for IDE and SATA drives. Easy to do with new Debian Sarge installer.
Don't make your problems my problems!
It's a disk redundancy technology and an insect killer.
The Linux Documentation Project has at least 3 free documents not infested with advertisement. Can I submit these too, one at a time??
That would at least given valuable comments and feedback to improve them.
No mention of hardware versus software RAID? I know the article is geared towards noobs, but I think they should've mentioned the pros and cons of hardware v. software.
-Rich
"1. RAID implementations on most consumer-grade motherboards (EIDE RAID with Promise controllers on-board, and so on) are cheezy. I've tried using them for several years now, and I ran into lots of unexplainable "glitches" that never occured when I took RAID out of the equation. (EG. The RAID array would suddenly report a failed drive, yet when I'd pull the drive out and try reformatting/reusing it on another machine as a stand-alone C: drive, it would have no problems at all and S.M.A.R.T. reported it was fine too.)"
I bought a KT7A-RAID when it came out (been something like 3-4 yers now I think) and it uses a Highpoint chip. I have never encountered any issues with the RAID config, I have used it for RAID0, RAID 1, and both.
Well I've wrestled with reality for thirty five years doctor, and I'm happy to say I finally won out over it.