[illumos-Developer] Changing sd_io_time to 8?

[Garrett D'Amore]

On Tue, 2011-05-03 at 14:51 +0200, Joerg Schilling wrote:
> Richard Elling <richard.elling at richardelling.com> wrote:
> 
> > I'd like to change sd_io_time from 60 (!) to 8.
> >
> > For those who are unfamiliar, sd_io_time is the default time before the sd driver
> > will timeout a command. By default, it will retry 3 or 5 times before failing the I/O.
> >
> > From http://src.illumos.org/source/xref/illumos-gate/usr/src/uts/common/sys/scsi/targets/sddef.h#1704
> >
> >     /*
> >     * 60 seconds is a *very* reasonable amount of time for most slow CD
> >     * operations.
> >     */
> >     #define	SD_IO_TIME			60
> >
> > Many RAID cards give up at around 8 seconds. Many HDDs guarantee some sort of response
> > in under 8 seconds (enterprise or RAID version).  If a consumer-grade drive can't get it's act 
> > together in 8 seconds, not much chance it will get any better in 60 seconds. Nobody cares about
> > 1x SCSI CD-ROMS circa 1989, except perhaps the SPARC folks :-) 
> 
> You seem to know too few about CD-ROMs... If they see a read error, they start 
> with internal retries and this is done at a really low speed - independent of 
> that you see on the advertizing for the drive.
> 
> If you lower this timeout, you increase the chance for aborting a command that 
> needs to be done anyway. As the sd driver has own retries, this may cause 
> things to fail that don't need to and in addition, you will need more time for 
> the whole operation (including sd retries).

This just underscores for me how terrible an idea it was to make
everything appear as a SCSI *disk*.  sd and sr should never have been
merged.  Sadly its too late to easily do anything about it.

	- Garrett