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I have a Dell 2600 with 6 drives configured in a RAID 5 on a PERC 4 controller. 2 drives failed at the same time, and according to what I know a RAID 5 is recoverable if 1 drive fails. I'm not sure if the fact I had six drives in the array might save my skin.

I bought 2 new drives and plugged them in but no rebuild happened as I expected. Can anyone shed some light?

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4 Answers 4

Regardless of how many drives are in use, a RAID 5 array only allows for recovery in the event that just one disk at a time fails.

What 3molo says is a fair point but even so, not quite correct I think - if two disks in a RAID5 array fail at the exact same time then a hot spare won't help, because a hot spare replaces one of the failed disks and rebuilds the array without any intervention, and a rebuild isn't possible if more than one disk fails.

For now, I am sorry to say that your options for recovering this data are going to involve restoring a backup.

For the future you may want to consider one of the more robust forms of RAID (not sure what options a PERC4 supports) such as RAID 6 or a nested RAID array. Once you get above a certain amount of disks in an array you reach the point where the chance that more than one of them can fail before a replacement is installed and rebuilt becomes unacceptably high.

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thanks robert I will take this advise into consideration when I rebuild the server, lucky for me I full have backups that are less than 6 hours old. regards –  bonga86 Sep 21 '10 at 15:00
    
If this is (somehow) likely to occur again in the future, you may consider RAID6. Same idea as RAID5 but with two Parity disks, so the array can survive any two disks failing. –  gWaldo Sep 21 '10 at 15:04
    
g man(mmm...), i have recreated the entire system from scratch with a RAID 10. So hopefully if 2 drives go out at the same time again the system will still function? Otherwise everything has been restored and working thanks for ideas and input –  bonga86 Sep 23 '10 at 11:34
    
Depends which two drives go... RAID 10 means, for example, 4 drives in two mirrored pairs (2 RAID 1 mirrors) striped together (RAID 0) yes? If you lose both disks in 1 of the mirrors then you've still got an outage. –  RobM Sep 23 '10 at 11:43
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Remember, that RAID is not a backup. No more robust forms of RAID will save you from data corruption. –  Kazimieras Aliulis May 31 '13 at 10:57

You can try to force one or both of the failed disks to be online from the BIOS interface of the controller. Then check that the data and the file system are consistent.

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Dell systems, especially, in my experience, built on PERC3 or PERC4 cards had a nasty tendency to simply have a hiccup on the SCSI bus which would know two or more drives off-line. A drive being offline does NOT mean it failed. I've never had a two drives fail at the same time, but probably a half dozen times, I've had two or more drives go off-line. I suggest you try Mircea's suggestion first... could save you a LOT of time. –  Multiverse IT Sep 21 '10 at 16:32
    
Thank you. Very useful details. –  Mircea Vutcovici Sep 22 '10 at 15:25
    
Hey guys, i tried the force option many times. Both "failed" drives would than come back online, but when I do a restart it says logical drive :degraded and obviously because of that they system still could not boot. –  bonga86 Sep 23 '10 at 11:27

Direct answer is "No". In-direct — "It depends". Mainly it depends on whether disks are partially out of order, or completely. In case there're partially broken, you can give it a try — I would copy (using tool like ddrescue) both failed disks. Then I'd try to run the bunch of disks using Linux SoftRAID — re-trying with proper order of disks and stripe-size in read-only mode and counting CRC mismatches. It's quite doable, I should say — this text in Russian mentions 12 disk RAID50's recovery using LSR, for example.

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It is possible if raid was with one spare drive , and one of your failed disks died before the second one. So, you just need need to try reconstruct array virtualy with 3d party software . Found small article about this process on this page: http://www.angeldatarecovery.com/raid5-data-recovery/

And, if you realy need one of died drives you can send it to recovery shops. With of this images you can reconstruct raid properly with good channces.

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