[illumos-Developer] Changing sd_io_time to 8?

[Joerg Schilling]

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).

Jörg

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