Hard drive rebuild time on MSA30

[JOHN NEMMERS]

Some learning moments and a question....

I have an MSA30 that is split in half (logically, that is).  One side for storage, the other for backup.  A drive failed on the backup side of the array.  That side has seven 320 GB drives set up as a RAID5 with a Hot Spare.  The Hot Spare kicked in like it should, but the rebuild was taking forever!  Learning moment: HP confirmed that the rule of thumb is 15 minutes per gig--telling me it would take 3.33333 days to complete the rebuild of the drive. 

When the drive failure occurred, I pulled the bad drive so I could order another.   The new drive came in some12 hours later (despite having a 24x7x4 care pack).   Since it was a Friday, I waited until Sunday night to replace the drive.  So Sunday night,  I slid it back into the slot-where the failed drive was located.  Rebuild was still going on with the Hot Spare.  Learning moment: Found out from HP (after the fact) that the rebuild should finish BEFORE replacing the drive.

 Be that as it may, the new drive took over for the Hot Spare and started rebuilding...at warp speed (Learning moment: replacing drives that failed in a storage array, rebuild and become a part of the original array--making the Hot Spare the Hot Spare again.  Given that, it made me wonder why you would wait to replace the failed drive until the Hot Spare is done rebulding--if it's only going to rebuild that drive immediately and put itself back into the array and make the Hot Spare the Hot Spare again....

The new drive in the original slot was done rebuilding in a little under three hours.

Learning moments aside, no matter how the HP tech tried to explain it, I couldn't quite understand why the new drive rebuilt so rapidly, while the Hot Spare was still crawling along with its rebuilding task after some 60 hours.

If anyone could shed some light on the dim recesses of my mind why the rebuild rates were so disparate, I would appreciate it.  My nagging feeling all along has been that maybe there was/is something wrong with the Hot Spare.

Thanks!

P.S. This thread has been moved from General to Storage Area Networks (SAN) (Small and Medium Business). - Hp Forum Moderator

[Dennis Handly]

>why you would wait to replace the failed drive until the Hot Spare is done rebuilding

Yes, that seems odd.  It just may be a rule of thumb?

>If anyone could shed some light on why the rebuild rates were so disparate,

Perhaps because:

1) The controller does the hot spare slowly so it doesn't slow down the normal I/O?

2) To rebuild RAID 5, the other 4 disks need to be read to compute the parity value.

    To copy from the hot spare, only one disk needs to be read?

[Johan Guldmyr]

Perhaps the rebuild priority setting could shed some light into 1)