Date: Mon, 21 Mar 2011 12:47:16 +0300 From: Sergey Gavrilov <srg.gavrilov@gmail.com> To: Paul Mather <paul@gromit.dlib.vt.edu> Cc: freebsd-stable@freebsd.org Subject: Re: ZFS - abysmal performance with samba since upgrade to 8.2-RELEASE Message-ID: <AANLkTinvKNXo%2B=xSgys0ds4vF_HyMfm-%2BwFDFdNTwLmG@mail.gmail.com> In-Reply-To: <F567E2A0-DCD7-4542-8851-53327223A87C@gromit.dlib.vt.edu> References: <4D660909.6090202@my.gd> <20110224075517.GA18146@icarus.home.lan> <AANLkTinke4TF8K_eP1LgmmSp7csv8Zxc=R1FQxfM3xFQ@mail.gmail.com> <F567E2A0-DCD7-4542-8851-53327223A87C@gromit.dlib.vt.edu>
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Yes, I know. But I have a lot of memory and I want it to be used if it improves performance. I tried to test whole system not just fs. And I surprised in why vfs.zfs.prefetch_disable="1" affects so much. 2011/3/18 Paul Mather <paul@gromit.dlib.vt.edu> > > On Mar 18, 2011, at 5:53 AM, Sergey Gavrilov wrote: > > > vfs.zfs.prefetch_disable="1" causes much slow read on sequence data in my > > case. > > > > with vfs.zfs.prefetch_disable="1": > > > > dd if=/pool1/test/idisk1 of=/dev/null bs=1m count=500 > > 524288000 bytes transferred in 18.347177 secs (28575949 bytes/sec) > > > > with vfs.zfs.prefetch_disable="0": > > > > dd if=/pool1/test/idisk1 of=/dev/null bs=1m count=500 > > 524288000 bytes transferred in 3.331806 secs (157358504 bytes/sec) > > > > after few seconds: > > dd if=/pool1/test/idisk1 of=/dev/null bs=1m count=500 > > 524288000 bytes transferred in 0.107767 secs (4865009592 bytes/sec) > > The last dd performance figures are undoubtedly reflecting a read from data > cached in RAM. You should do your test on a file that is bigger than your > RAM size, or at least bigger than the amount of RAM you are dedicating to > ARC. > > Other than that, ZFS prefetching *is* supposed to speed up sequential > accesses, so it's no surprise you notice a speedup in such cases. :-) > > Cheers, > > Paul. > > -- Best regards, Sergey Gavrilov
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