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Why RAID 5 Stops Working In 2009
Lally Singh recommends a ZDNet piece predicting the imminent demise of RAID 5, noting that increasing storage and non-decreasing probability of disk failure will collide in a year or so. This reader adds, "Apparently, RAID 6 isn't far behind. I'll keep the ZFS plug short. Go ZFS. There, that was it." "Disk drive capacities double every 18-24 months. We have 1 TB drives now, and in 2009 we'll have 2 TB drives. With a 7-drive RAID 5 disk failure, you'll have 6 remaining 2 TB drives. As the RAID controller is busily reading through those 6 disks to reconstruct the data from the failed drive, it is almost certain it will see an [unrecoverable read error]. So the read fails ... The message 'we can't read this RAID volume' travels up the chain of command until an error message is presented on the screen. 12 TB of your carefully protected — you thought! — data is gone. Oh, you didn't back it up to tape? Bummer!"
12 TB of your carefully protected â" you thought! â" data is gone. Oh, you didn't back it up to tape? Bummer!
If it wasn't backed up to an offsite location, then it wasn't carefully protected.
There are shills on slashdot. Apparently, I'm one of them.
I mean, WTF? Many people regard RAID as something magical that will keep their data no matter what happens. Well ... it's not.
Furthermore, for many enterprise applications disk size is not the main concern, but rather I/O throughput and reliability. Few need 7 disks of 2 TB in RAID5.
The Raven
The problem with Raid 5 is that the more drives you have the higher probability you have that more than one drive dies. That's why you have multiple raid 5 arrays of 4 disks maximum instead of one array of 7 disks.
If you use RAID to 'protect' your data, you clearly don't value your data at all.
While the interesting bit of this article is the coming demise of RAID 5, what you should be bringing away with it is, if RAID is all that stands between you and data loss, you're a noob.
When HDD's move to bigger sectors - there should be better error recovery reducing the probability of unrecoverable read errors. Right?
Not if what fails is the drive motor.
I can see a lot of people getting into a tizzy over this. The RAID 5 this guy is talking about is controlled by one STUPID controller.
There are a lot of methods, and patented technology that prevent just the situation he is talking about. Here is just one example:
RAID is not perfect, not by any stretch, but if you use it properly it will serve it's purpose quite nicely. If your data is that critical, having it on a single raid is ill advised anyways. If you are talking about databases, then RAID 10 is more preferable and replicating the databases across multiple sites, even more so.
What is this article about?
They say that since there is more data, you're more likely to encounter problems during a rebuild.
The issue isn't with RAID, it's with the file system. Use larger blocks/sectors.
Losing all of your data requires you to have a shitty RAID controller. A decent one will reconstruct what it can.
The odds of you encountering a physical issue increases as capacity increases, and decreases as reliability increases. In theory, the 1 TB and up drives are pretty reliable. Anything worth protecting should be on server-grade hard drives anyway.
The likelihood of a physical problem popping up during your rebuild is no higher with new drives than it was with old drives. I haven't noticed my larger drives failing at higher rates than my older, smaller drives. I haven't heard of them failing at higher rates.
Remember, folks, RAID is a redundant array of inexpensive disks. The purpose of RAID is to be fault-tolerant, in the sense that a few failures don't put you out of production. You also get the nice bonus of being able to lump a bunch of drives together to get a larger total capacity.
RAID is not a backup solution.
RAID 5 and RAID 6, specifically, are still viable solutions for most setups. If you want more reliability, go with RAID 1+0, RAID 5+0, whatever.
Choosing the right RAID level has always depended on your needs, setup, budget, and priorities.
Smells like FUD.
How many times does this have to be said.
RAID is not a backup. RAID is designed to protect against hardware failures. It can also increase your I/O speed, which is more important in some cases. Backups are different.
Depending on what you are doing, you may or may need a RAID, but you definitely need backups.
RAID 5, as well as RAID 6 is nothing more at an attempt to add some amount of redundancy without sacrificing too much space. Go RAID 1 instead with the same number of disks.
As far as I'm concerned, RAID 5 really has no redeeming features (it's slow, not particularly safe, but lulls people into a false sense of security).
From a data integrity perspective, though, RAID6 is a better solution than RAID1.
Given arrays of equal sizes, with RAID6 your data can survive the loss of *any* two disks; with RAID1, if you lose two disks which happen to be a mirrored pair, then you're hosed.
But, as you point out, RAIDn doesn't really qualify as "carefully protected"
Not everything that can be measured matters; Not everything that matters can be measured.
Scrub once a week, or once every two weeks.
RAID6 isn't about losing any two disks, it's about having two parity stripes. It's about being able to survive sector errors without any worry.
It's about losing ONE drive and still have enough parity to replace it without any errors.
RAID6 on 5 drives is retarded, tho, because it leaves you absurdly close to RAID1 in kept space. RAID6 is for when you have 8-10 drives. At that point you barely notice the (N - 2) effect and you have a fast (provided your processor can handle it all) chunk of throughput along with an incredibly reliable system. Well, N-3 with a hotswap.
Personally, I think I'd go RAID-Z2 via ZFS if only because it's a little bit sturdier a filesystem to begin with.
... very few people correctly cycle in new drives periodically to reduce the chance of a mass failure.
That is also because very few people buy a Raid setup piecemeal. Most end up buying a solution, fully populated. The idea of swapping out some drives as you go, or growing your RAID over time doesn't always look good, either to the PHBs who usually run the budget, or to the vendor. We had a vendor trying to sell us a iSCSI SAN device tell us that varying the drive lots and dates increased the chances of failure. Needless to say we went elsewhere.
When we bought the RAID array for our Exchange box, this is going back a few years, everybody looked at my like an idiot because I asked for drives with different lot numbers. It was the best I could do as buying over time was not an option. HP was actually pretty cool about this request and out of 8 disks, no 3 have the same lot number or manufacture date.
Of course we are also running RAID on that machine for non-backup and do a nightly replication, so your mileage may vary.
"To Do Is To Be" - Socrates, "To Be Is To Do" - Sartre, "Do Be Do Be Do" - Sinatra
Wow, how incite-ful. Doesn't matter what the discussion is, some geek is bound to weigh in with all the shortcomings of any idea.
Newsflash: there is no perfect backup! No method is foolproof, especially when it's bound to be boring as hell, and you've got an inevitable human factor. You get lazy moving the tapes offsite, you put off fixing a dead drive because there are 4 others, you wipe your main partition upgrading your distro and forget that your CRON rsync script uses the handy --delete flag, and BOOM wipes out your backup.
Shit happens. Pointing out what we all already know doesn't do anything helpful.
ad logicam Claiming a proposition is false because it was presented as the conclusion of a fallacious argument.
RAID-10 ftw? Expensive I know, but at least you have a full layer of redundancy rather than just a parity drive.
RAID doesn't protect against your worst enemy
rm -r *
nor is it supposed to. not being a moron seems to have protected me from "my worst enemy" just fine. RAID has protected me from random disk failures. seems to be working as designed
TIAEAE!
I'm in the process of building a new 8x 1T array. I'm not using any fancy raid card. Just a LSI 1068E chipset with a SAS expander to handle LOTS (16 slots in the case, using 8 right now).
I'm not putting the entire thing into one big array. I'm breaking up each 1T drive into ~100GB slices that I will use to build several overlapping arrays. Each MD device will be no more than 4-5 slices. This way if an error occurs on one disk in one part of a disk I will have a higher probability of recovery.
I may also use RAID 6 to give me more chance of rebuilding.
Disk errors tend to not be whole disk errors, just small broken physical parts of a single disk.
SMART will give me more chance to detect and replace dying drives.
Seriously - what's the problem with RAID 5? It's not a FALSE sense of security: It actually DOES prevent data loss or down time on a single disk failure. If you're a moron, you're creating 14 disk arrays. If you're smart, you keep it to 7 disks at the very most.
RAID 5 is great. It's fast, unless you have a shit controller without enough cache. It's going to prevent down time on a single disk failure (which is overwhelmingly the most common type of failure) and it doesn't cost you too much capacity.
Usually I'm more concerned with a fire or flood than a double-disk failure.
RAID 6 is good, but you get the same (actually worse) performance hit over RAID 5. More parity calculations. You can lose any two disks, which is nice, and if you can spare the space, go for it!
I don't see RAID 6 as being all that much more of a big deal over RAID 5 and actually it shouldn't really have it's own number since it's exactly the same technology and parity system as 5. It should be RAID 5.1 or something. Or maybe RAID5+1. The only reason it's become more available now is because controllers have gotten fast enough to deal with the additional parity.
- It's not the Macs I hate. It's Digg users. -
I guess you should be considered a new age Luddite?
Are you the same guy that always waits for SP1 before using any software? I thought so.
RAID is a proven technology and it's use in nearly all business IT systems from big to tiny.
RAID isn't meant as a replacement to backups. It's one PART of the entire system of preventing unnecessary data lose, and more importantly, down time. You can keep on running your server while the failed disk is replaced and rebuilt.
So, while I eat cheeto's and surf Slashdot while that RAID array rebuilds itself, you can go ahead and recover your old data from last night all day long while people bitch at you for not using the technology that's been around since the inception of the hard drive.
If you actually did have the experience you claim, you'd slap yourself for such a stupid fucking post.
- It's not the Macs I hate. It's Digg users. -
First off, Isn't this story a year+ old? Sheesh.
Second off, if you're worried about URE on X number of disks, what about a single capacitor cooking off on the raid controller? No serious data is stored on a single raid controller system, without good backups or another raid'd system on completely unique hardware. Yes, if you put a lot of disk on one controller and have a failure you have a higher risk of *another* failure. That's why important data doesn't depend on *only* RAID, and why lots of places use mirroring, replication, data shuttling, etc. This isn't new. Most folks that can't afford to rebuild from backups or from a mirror'd remote device also couldn't have used 12TB for anything *but* bulk offline file storage because it's slower than christmas VS a 'real' storage array. Using it for the uber HD DVR? Great. Oh no, you lose X-files's last episodes. This isn't banking data we're talking here.
Prioritize your data. I cannot believe that a home user has 12TB of important stuff. Back up your critical records both on site and off [1]. Back up the important stuff on site with whatever is convenient. Let the rest go hang.
[1] Use DVDs in the unlikely event you have that much critical data. Few home users will have a critical need for that stuff beyond the life of the media. Any that do can copy it over every five years, and take the opportunity to delete the obsolete stuff.
Warning: this article may contain humor, sarcasm, parody, and perhaps even irony. Read at your own risk.
Isn't it more cost effective to do RAID 1, with a nightly backup to an external. At least in my home, I do not require mission critical hot-swapping capabilities. Then again I only have 3x 1TB hard drives. Also, after RTFAing the author of the article assumes that an unrecoverable read error corrupts your RAID array. It does not, typically your bad sector gets added to the list and mapped out of being used. Speaking of used, article assumes that entire drive is being used, but if the error on the part of the drive not covered with data, this is also a non issue.
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The vast majority of Egypts writings were stored on perishable papyrus, not carved or painted on stone. Of all that they ever wrote or stored, we have but the tiniest fraction remaining.
If we lost technology today, there would be nothing left but paper in 20 years. In a thousand, there wouldn't even be much paper.
ad logicam Claiming a proposition is false because it was presented as the conclusion of a fallacious argument.
If you source the original term 'RAID', it goes to an ACM article describing Redundant Arrays of Inexpensive Disks. In RAID 0, which is actually a marketing term, there's striping, but no redundancy that can infer the contents of a missing member of the array. From the perspective of availability, it has none. As you cite, RAID 1 is a mirrored pair, usually the same type of drive, and it also is likely the fastest RAID-- and most expensive in terms of available net data after redundancy for availability. There is also no RAID 6...10, as these are marketing terms, too.
---- Teach Peace. It's Cheaper Than War.
"Shit happens. Pointing out what we all already know doesn't do anything helpful."
Actually, it gives posters like you a chance to remind everyone else that shit happens.
I believe there would be many fewer frustrated/bitter IT workers if more people meditated on the fact that shit just happens. In today's marketplace it is usually IT left holding the bag when things go south anyhow... gotta get acclimated to that and roll on.
Anyhow, I doubt there are many IT veterans not familiar with really expensive, really borked backup systems. Smarter people than me have observed that as technology progresses, existing strategies either age or mature. The ones that age become brittle, and the ones that mature become more robust...
Corporate suits usually insure that both aged and mature technologies will be flogged on long past their rational retirement dates.
RAID 5 will still be orders of magnitude more reliable than just having a single disk.
No sig today...
I do the same thing, but I want to warn you...
I've had TWO occasions where it has failed me. Once, a lightning strike that zotched both drives. The second time a rubber isolator failed in the case and the master drive fell onto the backup.
In both cases the bad spots in the two drives were different so I got back most of my data, but now I use Mozy as well as mirroring. I REALLLLLLLY don't want to lose all of my digital photos. :)
W..w..W - Willy Waterloo washes Warren Wiggins who is washing Waldo Woo.
Goodness, even the summary says "didn't back up? bummer!". Yes, we all know RAID only hedges against hardware failure. The point of this whole exercise is that RAID 5 doesn't even adequately help with hardware failures once data per drive grows large enough.
I'm glad the 'not being a moron' thing worked out for you. But, what would you suggest to those in the audience that cannot claim the same. :-)
OS X?
Even if it was feasible to buy all these hard drives or a tape drive, the amount of time it would take to properly do all these back-ups on a useful time scale seems to be beyond the reach of the typical user. Even power users do other things in their lives than worry about their computers. I can't see somebody with enough free time to make CD or DVD or tape backups every so often. And if you are copying your whole 1+ TB drive then it would take forever. It may just be that because I'm a college student I have less time than most people with normal jobs, but I see my dad come home late from work almost every day, and then he's just too tired to want to do anything else. So maybe this whole discussion just becomes irrelevant because not too many people realistically have the time to be able to do all this backing up, and would rather just take the risk of running a RAID setup.
Yes, that's what time machine is for. Sadly, my mac is the best backed up machine here. I have an external seagate drive hooked up with time machine and average around a month of backup points. I also burn things on DVD twice a year I can't live without like my iTunes collection. I really wish blu-ray would pick up on Macs for backup purposes. I could backup my iTunes with 3 50GB BD discs. 135GB of data to backup on 8GB DVDs?
Tapes are cost prohibitive and optical hasn't kept up with hard drive capacity. I remember when I could backup my whole computer on 2 CDs. Now, even with BD I'd need 5 discs.
Optical discs have their own problems, but I like to have backups on at least two different types of media. Since tapes are expensive and I've had terrible luck with them professionally, I'd like to stick to optical when possible.
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