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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.'"
There's an excellent guide to RAID levels (with pretty diagrams and such) at http://www.acnc.com/raid.html
http://en.wikipedia.org/wiki/Redundant_array_of_in dependent_disks
I've had my data corrupted by a dodgy controller... twice. I've been having terrible luck with the nvRAID provided on nVidia nForce 4 motherboards. Twice now the machine has locked up and on rebooting the RAID array is reported as damaged and a drive is missing from the array. A bit of Googling has revealed it's a common problem.
Fiddling around in the BIOS disabling and reenabling RAID makes both disks show up again but putting them back into a RAID array seems to do no good as Windows always claims files are missing after doing this. If I reinstall Windows my data is always all still there in perfect condition, the hassle of reinstalling Windows and my apps is a pain though. So it's not totally corrupted, but enough to be a complete bitch.
My feeling on RAID on the desktop is that it's a good idea but at least in nVidia's case it's being done on the cheap and is not totally stable. That said Intel's RAID controllers are superb and I'd use one anyday if it weren't for the vast amounts of heat and inferior performance of the P4.
... 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.
I've been using this board from Asus for about 6 months with onboard SATA RAID5. It cost $120 from Newegg.com when I got it, if my memory serves me.
Looks ok to me - not a single one. Want my AdBlock list?
Ads...I see them once in a while, but they are quickly added to my adblock list. Really, should tech saavy /. readers see very many ads at all? I think the poster of the parent is a wanna be geek. Ok, enough sluphing off, back to work...
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.
These days I think software raid is really the way to go, at least in comparison to the raid built into consumer grade raid cards. With software raid you should be able to move your disks to a working computer and boot up with a Knoppix CD and access your data if you have to. You can also raid individual partitions rather than entire disks. You could make a small non-raid boot partition on each disk which you sync regularly plus a larger data partition which becomes part of the raid.
The above applies to Linux, I don't think the non-server editions of Windows can do anything but raid 0 (maybe raid1?). Possibly a BartsPE CD could be used to recover a failed Win raid array.
I've been using software-RAID with ATA drives on Linux for quite some time, so I can comment on the behaviour of an array containing a faulty drive.
/dev/hdc, ATA error count increased from 0 to 1" and that it would be a good idea to check up on the hosts syslog.
/dev/md0 -a /dev/hdc1" the new one into the array, starting to resync it right away.
First off, let me emphasize how important it is to set up proper email notification (or pager etc.) for such cases! If you don't know about the failure, you're certain to get nice phonecalls from affected users.
If you've set up the notification system (smartd and mdadm come to mind), you'll eventually get an email saying something like "Device:
Checking up on the system, you'll find that the average system load has increased substantially, which is due to the system trying to persuade the disk to write to a faulty sector and the software RAID having to compensate, queuing the errors.
Depending on how often the defective sector is tried to be written to, the load can increase to values of 10 and above, rendering the system unusable. This is a good time to halt it and replace the defective drive, partition it and "mdadm
This may sound really horrible, but in practise it's usually less 60 minutes (counting from receipt of the first notification email) until normal operation can resume with such a system. This is assuming you have all spare parts stored somewhere on site.
In genereal, I've found software RAID1 and software RAID5 on Linux to be exceptionally stable. I'm also very happy about the performance, given that all I'm using is a bunch of el-cheapo ATA disks. As for reliability, I'm convinced it can't be beat in the consumers' price range, since I've seen too many consumer grade hardware RAID controllers go down in a swirl when putting more than a light load on them.
In the enterprise, I've seen companies move to software RAID on their Linux systems, because they found out that their only 5 years old enterprise hardware won't be getting any new spare parts anymore, which includes motherboards, CPU and IO controllers. Moving to software RAID on enterprise grade SCSI stuff allows them to move the entire system to another piece of hardware simply by moving the harddisk to it.
Forget all that. This is an excellent article on RAID.
http://arstechnica.com/paedia/r/raid-1.html