Date: Wed, 4 Apr 2018 20:04:32 +0300 From: Andriy Gapon <avg@FreeBSD.org> To: Stilez Stilezy <stilezy@gmail.com> Cc: freebsd-fs@freebsd.org Subject: Re: ZFS dedup write pathway - possible inefficiency or..? Message-ID: <a9a355a7-234e-2adf-bf6b-0cc9ffabf9d6@FreeBSD.org> In-Reply-To: <CAFwhr76%2B4G_ZVK1kHYvVegs1Oocdz3aPeqF3t%2BQtdsVmwtCmjg@mail.gmail.com> References: <CAFwhr76S-hqJya5P91HsJh94SnYR-scn%2BcmBEUFCDpQT_gD_OA@mail.gmail.com> <14c857cc-463f-a56e-bcf6-c0702da6d3bc@FreeBSD.org> <CAFwhr76%2B4G_ZVK1kHYvVegs1Oocdz3aPeqF3t%2BQtdsVmwtCmjg@mail.gmail.com>
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On 02/04/2018 21:30, Stilez Stilezy wrote: > Thanks on that tip, Andriy, > > I don't have the knowledge to tell if that's the first of the 2 issues I'm > seeing. It could be. What exactly is that bug describing and what behaviour > would it create? Sub-optimal performance for ZFS write throughput (and latency) when dedup is enabled and you are trying to write as fast as you can. > Assuming it's the same - > > 1) Are there any known workarounds or sysctls that help to reduce the issue? I don't know of any. > 2) Are there any easy diagnostic tests I can easily do, to confirm if this is > the same behaviour as that bug? Nobody else uses the test system, so I can > change any sysctls to sane or extreme values for testing, or create large txg's > and spread out reads and writes to see what's happening and what coincides with > what. We used DTrace to observe internal ZFS behavior. I do not have any simple recipes. > On 2 April 2018 at 18:47, Andriy Gapon <avg@freebsd.org > <mailto:avg@freebsd.org>> wrote: > > On 02/04/2018 16:36, Stilez Stilezy wrote: > > The first issue is specific to the > > dedup write pathway. I've tested locally to a point where it seems it's > > not due to inadequate hardware and it's very consistent and specific, even > > on idle conditions/minimal load. I'm wondering whether there's a code > > bottleneck specifically affecting just the dedup write pathway. > > I think that this might be https://www.illumos.org/issues/8353 > <https://www.illumos.org/issues/8353>; > > -- > Andriy Gapon > > -- Andriy Gapon
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