CAM//SCSI disk timeouts

[Kenneth D. Merry]

On Tue, Jan 20, 2004 at 13:18:00 -0800, Julian Elischer wrote:
> 
> 
> If we are talkign to a raid array and it discovers that it has to
> do some maintanance (e.g. declare a physical disk bad or recreate
> some data on the fly) it is possible that transactions to the raid
> that are outstanding may tak a lot longer than usual. In particular,
> we've seen the case where a log entry in teh Raid controller's log
> that indicates that a drive has been declared bad, is often accompanied
> in FreeBSD with a set of CAM /scsi-disk timeouts
> and things degrade from there...
> 
> Where can I find the  timeouts in force fo rscsi disks and teh retry 
> policies?
> 
> I need to compare the theoretical behaviour of FreeBSD CAM with the 
> theoretical timeouts needed for the raid array, given a disk failure..

You can tweak the timeout and retry count values with the
kern.cam.da.retry_count and kern.cam.da.default_timeout sysctl variables.

They are also available as loader tunables.

Ken
-- 
Kenneth Merry
ken at kdm.org