[illumos-Developer] Changing sd_io_time to 8?

[Joerg Schilling]

Richard Elling <richard.elling at richardelling.com> wrote:

> On Apr 30, 2011, at 6:59 AM, Mike La Spina wrote:
> > Hi Richard,
> >  
> > This would be a very beneficial change since a single failing sd device in a raidz1 seg would cause a 60 second delay in all IO for that seg.  I can see some potential for a negative impact in the VM world but if it?s tunable that?s really a non issue.
> > e.g
> >  
> > if VENDOR = VMware
> >  then
> > sd_io_time = 120  
>
> IIRC, I wrote an RFE for that about 10 years ago... don't recall the CR number, though.
> As you can see, for high availability systems (I was working with Sun Cluster at the time)
> the timeouts are critical. Similarly, for upper layers, like ZFS, that rely on the lower layers
> to handle errors, waiting 5 minutes to declare an HDD dead is unacceptable.
>
> Judging from some of the responses here, and a depressingly huge amount of misinformation
> on the 'net, the reset logic and control structure could use a good dose of exposure. I had done
> that analysis 10 years ago, and can redo today, but please give me a few weeks to pull it together.

It depends on what exactly happened. If the drive completely dies, you should 
be able to detect this in a different way and disable high level retries in the 
driver.

In cases where a drive becomes slow, it may still be better to be able to get 
the data and in case that there is a ZFS RAID on top of the drive, it makes 
sense to tell the driver to do a quick abort too.

Jörg

-- 
 EMail:joerg at schily.isdn.cs.tu-berlin.de (home) Jörg Schilling D-13353 Berlin
       js at cs.tu-berlin.de                (uni)  
       joerg.schilling at fokus.fraunhofer.de (work) Blog: http://schily.blogspot.com/
 URL:  http://cdrecord.berlios.de/private/ ftp://ftp.berlios.de/pub/schily