Why do I bother with RAID 10 ?

Before I post anything I just want to clarify what I mean by RAID 10 , this is sets of mirrored pairs that have been striped as against a RAID 0 which has been mirrored.

I've just had a disk failure in the data array for one of my dev servers, it's an eight disk raid 8, no real worries, replace disk and off we go - but no - the HP engineers told me from the diagnostics ( done to ensure I got the right replacement under warranty ) that not only had a disk failed but I'd lost all the data on the array. Fair enough, once I'd replaced the disk all the database mdf files were inaccessible - not an issue as I have backups but it's still a bit of  a pain restoring 14 odd databases, the system databases were ona different array.

Now the point here is that in my time as a DBA I've only ever suffered a few disk failures and I've generally been using raid 10 since the days of SQL Server 6.0, every failure of a disk in a RAID 10 has resulted in the loss of the array/data, OK  this is only the 4th time in 16 years but it's still a pain. Now I've tested array builds - not for those of a nervous disposition - where I've pulled disks out of running arrays and replaced them to see what happens ! Happily the arrays rebuilt and no data was lost - I would say that on a large array if it's RAID 5 and the slower the disks the longer the rebuild will take, in fact a rebuild of a RAID 5 almost makes the array unusable and it may take many hours. RAID 10 in my experience suffers very little during the rebuild.

However I wonder if I really need to use RAID 10, especially for non production boxes, no the answer isn't to use RAID 5 as the write overhead is horrible, but my 1.2TB RAID 10 would be 2.4TB RAID 0 and I'd double up the iops/speed/throughput by having 8 spindles available insterad of 4 and I'd have more availble space - as long as I had backups I'd be in the same position as if I had 10.

Food for thought ?

Published Friday, April 23, 2010 7:44 AM by GrumpyOldDBA

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# re: Why do I bother with RAID 10 ?

Friday, April 23, 2010 2:03 PM by tonyrogerson

I use RAID 0 for dev/test boxes now so - no brainer; the developers have big enough local disks if it all goes pair shaped.

Sounds like the guy goof'd up and removed the partition or something.