Messages in this thread | | | Date | Thu, 29 May 2008 17:08:59 -0400 (EDT) | From | Justin Piszcz <> | Subject | Re: Performance Characteristics of All Linux RAIDs (mdadm/bonnie++) |
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On Thu, 29 May 2008, Kasper Sandberg wrote:
> 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 > stable? Not off-hand, check LKML and my email address from early this year or last year and/or the ide-list.
Justin.
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