[CentOS] KVM Host Disk Performance

Mon Apr 4 18:58:19 UTC 2011
John R Pierce <pierce at hogranch.com>

On 04/04/11 11:32 AM, Chuck Munro wrote:
> I'd love to hear what other software RAID users think, especially
> regarding large-capacity drives.  It's rare for a modern drive to hand
> out bad data without an accompanying error condition (which the md
> driver should handle), but I have read that uncaught bad data is
> possible and would not be flagged in RAID arrays which don't use parity
> calculations.

AFAIK, no standard raid modes verify parity on reads, as this would 
require reading the whole slice for every random read.  Only raid 
systems like ZFS that use block checksuming can verify data on reads.   
parity (or mirrors) are verified by doing 'scrubs'

Further, even if a raid DID verify parity/mirroring on reads, this would 
at best create a nonrecoverable error (bad data on one of the N drives 
in the slice, no way of knowing which one is the bad one).