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replace drive in RAID 5 array

Posted on 2007-11-15
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i have a RAID 5 array consisting of drives 1-4, and drive 0 which is a hot fix. now drive 4 has broken (red light in the array, log copied below) and drive 0 has 'stepped in', the system is saying 'missing hot fix'.
 
i assume i need to replace the dead drive 4 with a new HDD, make it part of the array again and then revert drive 0 back to being the hot fix. my hardware support guy's reply is 'just replace dead drive 4 and make it a hot fix'. is this correct? surely that will change the arrangement of the array making drive 4 as the hot fix, rather than drive 0 which it always has been. shoud i do this?

what is the correct procedure for replacing the broken drive 4 and having a hot fix drive, and through what interface do i do the fix (SCSI BIOS, Storage console or storage console plus?).

LOG COPIED FROM STORAGE CONSOLE:
  0 Mon Nov 05 10:01:05 2007   1  13 Array Drive 1: Logical Drive 4 <SCSI-A, ID 4, LUN 0> failed

  0 Mon Nov 05 10:01:05 2007   1  14 Array Drive 1: FAIL state entered

  0 Mon Nov 05 10:01:25 2007   1  22 Array Drive 1: Hot Fix 0 activated

  0 Mon Nov 05 10:01:25 2007   1  16 Array Drive 1: failed drive replaced by Logical Drive 0

  0 Mon Nov 05 10:01:25 2007   1  41 SCSI-A, ID 4: Auto Hot Plug for Hot Fix started for slot 4

  0 Mon Nov 05 10:01:25 2007   1  26 Array Drive 1: drive rebuild started

  0 Mon Nov 05 12:59:55 2007   1  21 Array Drive 1: drive rebuild finished successfully


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Question by:Pete
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by:cuziyq
ID: 20292031
The hardware treats everything as a logical device and abstracts the physical devices for you.  Translation -- the controller can keep it straight regardless of what slot the hot spare is in.  All you have to do is make sure that the new hot spare is configured as a member of the array.  You can do this through the SCSI BIOS or the software management tool.  Id doesn;t really matter.  SCSI RAID arrays are remarkably flexible like that.

FYI, you might want to mark the new hot spare, however.  Even though the array knows which drive is which, it's probably not the leftmost or rightmost drive in the anclosure anymore :-).  If you ever decide to remove it, you don't want to trigger another rebuild by removing the wrong one.
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by:Pete
ID: 20292182
thanks, what a fantastic and speedy reply, a few last Q's to clarify my actions tomorrow morning:

- can i leave the server running while replacing the drives (preferable)?
- do i need to 'remove' the drive in the software before physically removing from the server?
- once the new drive is in the server, i understand (from the manual) I right click the array in the software and simply select 'add hot fix' i then choose the new drive which should be the only one offered to me.
- job done?

any comments, corrections gratefully received.
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cuziyq earned 500 total points
ID: 20292630
Well, if you plan on having the hot spare in a specific position within the enclosure for the sake of neatness (either on the leftmost or the rightmost slot) then yes you will have to bring down the server because if you do it while the server is running, it will trigger a fault.  (If you do decide to bring down the server and rearrance the drives to your liking, the controller will not care and you shouldn't have to reconfigure anything).  But if you don't care about neatness, then no you do not have to bring down the server at all -- as long as you only intend to pull the defective drive.

Now, as far as removing the defective drive from the configuration, it all depends on the controller and the software.  Most will simply recognize the new hot spare as soon as it's replaced and you won't have to configure anything.  Some do not, however and will require you to manually add a hot spare back into the fold.  Even if that were the case, you don't have to worry about the order.  You can configure the new hot spare first and then remove the old one if it's still hanging around.  My guess is that it wouldn't, though.

The goal for array software is bare minimum administrative effort.  The software should be smart enough to know that the array after the failure should look the same as it did before the failure.
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by:cuziyq
ID: 20292634
Let me know how it goes for you :-)
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by:Pete
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speedy..
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by:Pete
ID: 20296968
It really was as simple as replacing the drive, the array automatically added the new drive as a hot fix, no user intervention was required. I have labelled drive 4 as my new hot fix.

Thanks for all your help with this.
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