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Recovering a Wrecked RAID
Dr. Eggman writes "Tom's Hardware recently posted an article specifying how the professionals at Kroll Ontrack recover data from a RAID array that has suffered a hard drive failure, allowing for recovery of even RAID 5 arrays suffering two failures. The article is quick to warn this is costly, however, and points out the different types of hard drive failures that occur, only some of which are repairable. Ultimately the article concludes that consistent backups and other good practices are the best solution. Still, it provides an interesting look into the world of data after death."
For DB's and home use a mirror set is usually best. For homes because it is simple, for DB servers because it is fast.
My home setup is a pair of 300 gig drives in a mirror, with another 1.6TB for other storage. Stuff that is important is on the mirror, and is differentially backed up to DVD regularly.
Stuff on the mass array is available in original form (my DVD and CD library that's been ripped) or is backed up whenever it changes, which is not often (my code library, for example). Active code and my wife's thesis are on the raid. Supporting documents for the thesis are on DVD and mass storage, as is old code projects that I may borrow from for functionality in a new project. The old project (and likely several versions of it) are off on DVD in a safe deposit box, with the rest of my backups.
Safe deposit boxes are awesome. I have one that can store 600 cds in cake boxes and it only costs $120/year. Dirt cheap for climate controlled fireproof storage.
-nB
whois gawk date unzip strip find touch finger mount join nice man top fsck grep eject more yes exit umount sleep dump
RAID 50? Why not RAID 10? If you're already mirroring, the RAID 5 will probably not afford you much additional protection, and it has the effect of making writes slower.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
It takes far too many pages to say what could actually fit in a page or two.
Never put all of your eggs in one little basket (RAID or otherwise)! For the love of God, if your data is critical, you need a backup *and* an offsite backup. At least one of each. There are no exceptions to this rule.
Could these articles be any more annoying to read?
They painstakingly
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pull data
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off the
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damaged drive
I have a concern with the recommendations given in the introduction:
We assume that all hard drives will be handled with care, so they should be installed in suitable drive bays. If you use multiple drives, we recommend removable drive frame solutions, which help reduce vibration transfer onto the computer chassis and even back to individual hard drives. Make sure that your system has sufficient ventilation, so high speed hard drives won't overheat.
I've found that the removable drive frames available for cheap consumer hardware to be total crap. The metal enclosure keeps heat close to the drive, and the tiny fans used don't move nearly as much air past the drive as when it's inside the case, being cooled by the airflow of the case fans. The drive temperature is therefore higher even under the best conditions. In addition, the smaller fans fill with gunk quickly and as a result wear out faster than larger ones, leading regularly to a drive trapped in an uncooled box.
I've used enclosures from Promise, Enermax, and several other companies whose products were so bad I tried to forget their names; all had fans that instantly became the least reliable part of the entire system once I installed the drive frame, and I wasn't happy with the drive's temperature from day one.
I don't think the person making this comment at Tom's ever keeps systems running long enough to realize the long-term issues that come with anything cheaper than server-grade drive enclosures for hard drives. I'd welcome suggestions for a better quality product in this category. It's a hard subject to cover, because by the time you've had several units setup for a year or two to gather useful data on how rugged they are, the product is obsolete; not something any review site I'm aware of is setup to cover.
Guys, if you're doing regular backups and have a cold spare handy then RAID5 is typically more than enough. Two drive failures are exceedingly rare unless you have some sort of controller fault (and that will typically hit all of your drives anyway). Don't forget about the write penalty either, RAID 5 has a fairly stiff penalty, but RAID 6 is even worse. If you're talking about RAID5_0 or RAID6_0 you're almost certainly doing it wrong or planning for a day when you can't buy replacement hard drives (nuclear holocaust?).
To put it another way: What do you think your chances are of having a second drive failure in the few hours it takes you to replace the drive and rebuild it? Even if that does happen you just lose the data up until your last backup (a day at most).
Most professional installations I do are RAID1_0, because people are building the RAID array for the performance, not the cost. Since you're using crappy 80GB HDDs, I'm guessing you're going for cost, which makes it strange that you're thinking about a RAID6_0 solution at all (the controller alone won't be cheap for that). If you work the odds I think you'll find that it's just not worth it to build a RAID6_0, especially given the write penalty and complexity (complexity is your enemy with this, complexity means bugs, which can undermine your entire effort).
I read the internet for the articles.