taskqueue timeout

[Andrew Snow]

Matthew Dillon wrote:
>     Try that first.  If it helps then it is a known issue.  Basically
>     a combination of the on-disk write cache and possible ECC corrections,
>     remappings, or excessive remapped sectors can cause the drive to take
>     much longer then normal to complete a request.  The default 5-second
>     timeout is insufficient.

 From Western Digital's line of "enterprise" drives:

"RAID-specific time-limited error recovery (TLER) - Pioneered by WD, 
this feature prevents drive fallout caused by the extended hard drive 
error-recovery processes common to desktop drives."


Western Digital's information sheet on TLER states that they found most 
RAID controllers will wait 8 seconds for a disk to respond before 
dropping it from the RAID set.  Consequently they changed their 
"enterprise" drives to try reading a bad sector for only 7 seconds 
before returning an error.

Therefore I think the FreeBSD timeout should also be set to 8 seconds 
instead of 5 seconds.  Desktop-targetted drives will not respond for 
over 10 seconds, up to minutes, so its not worth setting the FreeBSD 
timeout any higher.


More info:
http://www.wdc.com/en/library/sata/2579-001098.pdf
http://en.wikipedia.org/wiki/Time-Limited_Error_Recovery



- Andrew