[CentOS] DegradedArray message

[John R Pierce]

On 12/2/2014 6:24 PM, Fred Smith wrote:
> In reality, I had (in my ignorance) purchased a pair of WD
> drives that aren't intended to be used in a RAID array, and
> once in a long while (that was actually the only such instance
> in the 4-5 years I've had that RAID array) it doesn't respond to
> some HD command or other and gets dropped.

desktop class SATA drives will report 'write successful' when there's 
still data in its buffers, so the raid will happily continue, then if 
the drive actually gets a unrecoverable write error, things are toast, 
the raid is out of sync.

this is a major reason I'm leaning towards using ZFS for future raids 
(primarily via using FreeBSD), because ZFS checksums and timestamps 
every block it writes, so it can look at the two blocks that a regular 
raid can only say "something is wrong here, but what it is I ain't 
exactly sure" and go "A is good, B is bad/stale, lets replicate A back 
to B", as part of the zpool 'scrub' process.


-- 
john r pierce                                      37N 122W
somewhere on the middle of the left coast