[OpenIndiana-discuss] ZFS & SMART error

[Richard Elling]

On Jul 6, 2012, at 12:59 AM, Richard L. Hamilton wrote:
> 
> It's been my impression on a few occasions that a disk with very limited damage might have any bad areas discovered and effectively repaired by a scan; even on a semi-modern (e.g. older Fibre Channel) disk, the manufacturer's and grown defect list can be extracted, for example; and even when the disk itself handles sparing, a scan might force it wherever needed.  However...if a disk's surface has taken damage, there's always the chance that its internals were polluted with the debris, or the area damaged is irregular enough to lead to further damage.  So I certainly wouldn't trust a disk that gave ANY significant indication of failure for any purpose in which it was critical...whether for mechanical damage or wonky electronics or firmware doesn't even matter, in the long run.  (A glitch or two after a power failure, ok, but not continuing to increase afterward.  I would think most modern disks are able to manage a soft landing as it were in case of power failure, minimizing the risk of _mechanical_ damage, although noise might scramble any data being written at the time.)

SMART disks periodically do media scans. This was not the case years ago, when it was
more common to have format scan and repair commands in the frontal lobe of systems
administrators.

> It's not 100% clear to me (from the man page, i.e. no time to try to figure it out from the code now) whether zpool scrub examines free blocks as well as blocks that are in some way in use; if not, then a scan with format could potentially spot additional problems.

zpool scrub only checks data, it does not check unused portions of the disk.
 -- richard

--
ZFS Performance and Training
Richard.Elling at RichardElling.com
+1-760-896-4422