[illumos-Developer] Changing sd_io_time to 8?

[Garrett D'Amore]

On Thu, 2011-05-05 at 12:15 +0200, Joerg Schilling wrote:
> "Garrett D'Amore" <garrett at nexenta.com> wrote:
> 
> > I think we can be smarter here too.
> >
> > CDROMS need a longer recovery time.
> >
> > Disks on Parallel SCSI might need longer.
> >
> > Disks on fibre, SAS, and SATA, should all respond within a narrow window
> > of time unless something is seriously amiss.
> 
> There is no difference between Parallel SCSI and other SCSI transports besides 
> just the transport itself.

The issue here is extra timing required because of problems typically
found on parallel scsi transports.  One example of this is incorrectly
terminated busses which can cause large delays.  The other issue is that
disks on such busses are usually older, as are the hbas, and so are more
likely to "struggle" (at least in my experience.)

> 
> A hard-disk that is just booting after a power on or reset and that has read 
> problems in one of the copies for the firmware sectors or in one of the copies
> for the defect list sectors may take a _long_ time too to recover and it is of 
> course worth to wait at least a minute in such a case.

An interesting point.  I've never seen this particular failure mode
before.

> 
> If you really like to speed things up, start thinking about a way to reduce the 
> number of driver level _retries_ in case of problems if the related disk is 
> part of a RAID-Z2 and the dataa could be recovered otherwise.

That's a reasonable idea.

	- Garrett
> 
> Jörg
>