Date: Wed, 27 Nov 2013 12:36:58 +0000 From: Tom Evans <tevans.uk@googlemail.com> To: Richard Kojedzinszky <krichy@cflinux.hu> Cc: FreeBSD FS <freebsd-fs@freebsd.org> Subject: Re: ssd for zfs Message-ID: <CAFHbX1L60Mz0_2MieXa80QbW1CgKkn2Q1g%2B278Of-d1fAqvL2A@mail.gmail.com> In-Reply-To: <alpine.BSF.2.00.1311270946260.70091@pi.nmdps.net> References: <alpine.BSF.2.00.1311270946260.70091@pi.nmdps.net>
next in thread | previous in thread | raw e-mail | index | archive | help
On Wed, Nov 27, 2013 at 8:51 AM, Richard Kojedzinszky <krichy@cflinux.hu> wrote: > Dear fs developers, > > Probably this is not the best list to report my issue, but please forward it > to where it should get. > > I bought an SSD for my ZFS filesystem to use it as a ZIL. I've tested it > under linux, and found that it can handle around 1400 random synchronized > write IOPS. Then I placed it into my freebsd 9.2 box, and after attaching it > as a ZIL, my zpool only performs 100 (!) write iops. I've attached it to an > AHCI controller and to an LSI 1068 controller, on both it behaves the same. > So I expect that something in the scsi layer is different, FreeBSD is > handling this device slower, but actually it can handle the 1400 iops as > tested under linux. > > Please give some advice where to go, how to debug, and how to improve > FreeBSD's performance with this drive. > The ZIL is only used for synchronous writes. The majority of writes are asynchronous, and the ZIL is not used at all. Plus, a ZIL can only increase iops by bundling writes - if your underlying pool is write saturated already, then a ZIL can't help - any data written to the ZIL has to end up on the pool. Test the SSD by itself under FreeBSD to rule out FreeBSD not working correctly on the SSD (I doubt this though). Cheers Tom
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CAFHbX1L60Mz0_2MieXa80QbW1CgKkn2Q1g%2B278Of-d1fAqvL2A>