Messages in this thread | | | Date | Wed, 28 May 2008 15:27:58 -0400 (EDT) | From | Justin Piszcz <> | Subject | Re: Performance Characteristics of All Linux RAIDs (mdadm/bonnie++) |
| |
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?
But FYI-- In this test, they were regular SATA drives, not special raid-ones (RE2,etc).
Thanks for the info!
Justin.
| |