On Wed, 2008-05-28 at 15:27 -0400, Justin Piszcz wrote:
> On Wed, 28 May 2008, Chris Snook wrote:
> > Justin Piszcz wrote:
> >> On Wed, 28 May 2008, Chris Snook wrote:
> >>> Justin Piszcz wrote:
> >>>> Hardware:
> >>> Given that one of the greatest benefits of NCQ/TCQ is with parity RAID,
> >>> I'd be fascinated to see how enabling NCQ changes your results. Of
> >>> course, you'd want to use a single SATA controller with a known good NCQ
> >>> implementation, and hard drives known to not do stupid things like
> >>> disable
> >>> readahead when NCQ is enabled.
> >> Only/usually on multi-threaded jobs/tasks, yes?
> > Generally, yes, but there's caching and readahead at various layers in
> > software that can expose the benefit on certain single-threaded workloads
> > as
> > well.
> >> Also, I turn off NCQ on all of my hosts that has it enabled by default
> >> because
> >> there are many bugs that occur when NCQ is on, they are working on it in
> >> the
> >> libata layer but IMO it is not safe at all for running SATA disks w/NCQ as
> >> with it on I have seen drives drop out of the array (with it off, no
> >> problems).
> > Are you using SATA drives with RAID-optimized firmware? Most SATA
> > manufacturers have variants of their drives for a few dollars more that
> > have
> > firmware that provides bounded latency for error recovery operations, for
> > precisely this reason.
> I see--however, as I understood it there were bugs utilizing NCQ in libata?
You wouldnt happen to have some more information about this? i havent
personally had problems yet, but i havent used it for very long - but
since it comes activated by DEFAULT, i would assume it to be relatively
> But FYI--
> In this test, they were regular SATA drives, not special raid-ones (RE2,etc).
> Thanks for the info!
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