On 11/11/13 09:36, Stan Hoeppner wrote:

On 11/10/2013 2:34 PM, NeilBrown wrote:

quoted

The firmware can only relocate a sector if it reads it when it is marginal
but not yet completely lost.  If a sector is not read for a long time and
during that time the media degraded beyond recovery the firmware cannot do
anything.  But RAID1 can - it can get it from the other device.

But is a scrub required for this?  Isn't this exactly what occurs during
normal operation with md/RAID1?  I.e. a read fails with disk error, so
we grab the sector from the mirror?  So what advantage is there to
scrubbing md/RAID1?

Wouldn't a check of the raid cause each member to be read in full, 
therefore helping the disk to notice that the sector is marginal, and/or 
the RAID layer to notice that the sector is no longer readable and 
therefore read from the other member, and re-write the sector. Consider 
a sector that is very rarely accessed...

Or are you suggesting that a smart command issued to the underlying 
devices can solve both of those scenarios?

Regards,
Adam

-- 
Adam Goryachev Website Managers www.websitemanagers.com.au