On Sun, 10 Nov 2013 16:36:35 -0600 Stan Hoeppner [off-list ref]
wrote:

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

quoted

On Sun, 10 Nov 2013 13:17:21 -0600 Stan Hoeppner [off-list ref]
wrote:

quoted

Also, I see little/no value in running a scheduled mdadm check on a
RAID1 array.  Any problems with RAID1 will be due to one of the disks
beginning to fail in some mode, usually requiring sector relocation.

I think scrubbing has value on any RAID with redundancy.

That's a bit... redundant, Neil. :)

RAID0.  Sadly a name that is used, even though it is an oxymoron.

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?

If scrubbing finds and repairs a (rarely accessed) bad sector on one drive
before the other drive dies completely, that is a win.

NeilBrown