Date: Tue, 11 Mar 2014 15:48:56 +0000 From: Tom Evans <tevans.uk@googlemail.com> To: Danny Schales <dan@latech.edu> Cc: FreeBSD Stable <freebsd-stable@freebsd.org> Subject: Re: ZFS UNMAP performance Message-ID: <CAFHbX1JghVaQ3xM2OZ6jpWOs6tn=Z8epd8Om3NW_CDnZHPSdng@mail.gmail.com> In-Reply-To: <531F2BA0.6000105@LaTech.edu> References: <531F2BA0.6000105@LaTech.edu>
next in thread | previous in thread | raw e-mail | index | archive | help
On Tue, Mar 11, 2014 at 3:28 PM, Danny Schales <dan@latech.edu> wrote: > I'm seeing very slow performance with certain operations on a ZFS > filesystem built on ISCSI LUN's on a 10.0 system (new ISCSI > implementation). The issue appears to be with BIO_DELETE operations. > Monitoring the system with gstat shows expected times for read and write > operations, but deletes are in the multiple hundreds of milliseconds > under normal operation. Destroying a snapshot sends the times to > astronomical levels. sysctl says the system is using UNMAP for deletes: > > kern.cam.da.0.delete_method: UNMAP > > I searched and found where Oracle issued a performance alert for Solaris > 11.1 where ZFS using UNMAP was in use. Here's a link to a blog > discussing it: > > http://schalwad.blogspot.com/2013/12/solaris-111-zfs-write-performance.html > > > Is FreeBSD also impacted? If so, is there a fix or a workaround? FreeBSD is affected the same way Solaris is. IMHO, neither are affected, it is merely a consequence of using a device with a poor TRIM/UNMAP algorithm. You can trivially tell ZFS to not use TRIM, or tweak the tunings to suit your devices. I'm afraid I don't know what they all mean precisely.. vfs.zfs.vdev.trim_on_init: 1 vfs.zfs.vdev.trim_max_bytes: 2147483648 vfs.zfs.vdev.trim_max_pending: 64 vfs.zfs.trim.enabled: 1 vfs.zfs.trim.txg_delay: 32 vfs.zfs.trim.timeout: 30 vfs.zfs.trim.max_interval: 1 Of course, if you disable TRIM you will end up with new (but different) poor performance characteristics. Probably. Cheers Tom
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CAFHbX1JghVaQ3xM2OZ6jpWOs6tn=Z8epd8Om3NW_CDnZHPSdng>