Date: Sun, 24 Nov 2013 09:03:24 +0100 From: Thomas Steen Rasmussen <thomas@gibfest.dk> To: Eitan Adler <lists@eitanadler.com> Cc: "freebsd-fs@freebsd.org" <fs@freebsd.org> Subject: Re: ZFS (or something) is absurdly slow Message-ID: <5291B2CC.2040907@gibfest.dk> In-Reply-To: <CAF6rxgkPVDnmS1RTugLVYUP3H6=Azjx%2BsgYv91_6d0yAg6Gthw@mail.gmail.com> References: <CAF6rxgmepSN9pFPH%2BQiLaNqhzXxkXwu=59zvfD-6gGEMg9zh1g@mail.gmail.com> <5290E0CF.20704@gibfest.dk> <CAF6rxgkPVDnmS1RTugLVYUP3H6=Azjx%2BsgYv91_6d0yAg6Gthw@mail.gmail.com>
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On 24-11-2013 04:15, Eitan Adler wrote: > >> vfsstat.d https://forums.freebsd.org/showpost.php?p=182070&postcount=6 > I can run this script, what output should I be looking for? Check the sample output on the page: It shows two lists, "Number of operations" and "Bytes read or write". The lists are ordered with the busiest at the bottom and seperated by filesystem location. While things are slow, try running it to see if some location on the filesystem is being hammered. One case I had was where /home/pgsql/data was the culprit, due to the default sync setting in postgres, along with a malfunctioning webapp that kept making a lot of queries. This activity wasn't shown with "top -m io -o total" for some reason. Another thing you should probably do is run a SMART check on the disk to see if something is wrong with it. I had another case with a zfs mirror that performed appalingly, turned out it was because one of the disks was dodgy, not in a way that made zfs show checksum errors, but enough to make it really really slow. Since a ZFS vdev only performs as good as the slowest disk in a vdev, which in turn will slow the whole pool down, replacing the disk made everything much better. What does diskinfo -ct /dev/whatever say about the seek times on the bad disk ? Are the results the same if you boot off of an usb stick and test the disk when it is completely idle and independent of the running OS ? /Thomas
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