Comments on: SSD Migration in the Enterprise Environment

By: Andreas Erson

Andreas Erson — Thu, 24 Feb 2011 09:43:37 +0000

In reply to Noel. Interesting, what controller are you using? If eight 2-disk groups is a raid 10 then two 8-disk groups is a raid 01. If you can handle loosing 8 drives in a disk group that means the mirroring must be between the disk groups (thus being raid 01) or that you have eight 2-disk mirrors with each mirror having one disk in each of the two disk groups.

By: Noel

Noel — Wed, 23 Feb 2011 14:17:18 +0000

In reply to Andreas Erson. Andreas, I see what you mean now. I should have worded it differently for clarity. It will be edited shortly. I appreciate your feedback.

By: Noel

Noel — Wed, 23 Feb 2011 13:27:26 +0000

Andreas, I run 8 disks in each disk group, with 2 disk groups. Two disk failures in a single DG would not cause me to lose data, even four or 8 wouldn’t. How do I know this? I’ve tested it extensively before rolling it out into production. Most enterprise-grade RAID controllers allow you to choose how many disks you want in each disk group when building your RAID10 disk groups. Most controllers would default to eight 2-disk groups, but I felt that wasn’t enough protection, and that is why I chose two eight-disk groups.

By: Andreas Erson

Andreas Erson — Wed, 23 Feb 2011 09:11:27 +0000

In reply to Noel. Noel, I'm fully aware of the way a RAID 10 works. In your 16-drive scenario you have 8 mirrors that are then striped. I don't see the relevancy of pointing that the likelihood of over half of the drives failing at the same time is extremely remote without mentioning that in a worst case scenario it's enough that two drives in the same mirror fails for you too loose all the data in your 16-drive array.

By: Noel

Noel — Mon, 21 Feb 2011 13:38:12 +0000

In reply to Andreas Erson. Actually, Andreas, RAID10 is simply striped groups of RAID1(mirrors). In RAID10, all but one drive from each RAID 1 group could fail without damaging the data.