[OpenIndiana-discuss] ZFS's vdev state transition

[Richard Elling]

On Jul 20, 2012, at 12:01 PM, Bob Friesenhahn wrote:

> On Fri, 20 Jul 2012, Ichiko Sakamoto wrote:
> 
>> Hi, all
>> 
>> I have a disk that has many bad sectors.
>> I created zpool with this disk and expected that
>> zpool told me the disk has meny errors.
>> But zpool told me everything was fine until I scrubbed the zpool.
>> 
>> Is this designed feature?
> 
> Zfs detects hardware-reported write failures, but can/does not detect read failures until it tries to read the data.  I have learned that zfs does periodically "taste" the data in a few locations as part of normal operation (to detect disk errors) but it tries to read from the disk as seldom as possible since doing so would hinder performance.

Write errors are also detected. In the fmdump output we see a fatal write due to
media error. ZFS can and does work around this by re-allocating the write, but
it should be ticked in the write errors column.

> If the disk continually reports that all writes are fine then zfs might not discover wrong data for a long time, or until 'scrub'.

Correct. Again, this case is interesting because the reads are counted as 
checksum errors, but not read errors. But until we know what version of the
OS is being used, we can't debug any further.
 -- richard

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