Date: Wed, 27 Nov 2013 14:07:01 +0100 (CET) From: Richard Kojedzinszky <krichy@cflinux.hu> To: Tom Evans <tevans.uk@googlemail.com> Cc: FreeBSD FS <freebsd-fs@freebsd.org> Subject: Re: ssd for zfs Message-ID: <alpine.BSF.2.00.1311271404300.53767@pi.nmdps.net> In-Reply-To: <CAFHbX1L60Mz0_2MieXa80QbW1CgKkn2Q1g%2B278Of-d1fAqvL2A@mail.gmail.com> References: <alpine.BSF.2.00.1311270946260.70091@pi.nmdps.net> <CAFHbX1L60Mz0_2MieXa80QbW1CgKkn2Q1g%2B278Of-d1fAqvL2A@mail.gmail.com>
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Dear FS devs, After some investigation, it turned out that when I turn write-cache off under linux, the performance drops to 100 on that OS also. But when enabled, 1400 IOPS (synchronous) can be achieved. So I would like to see the same on FreeBSD as well. Using camcontrol shows that the write cache is enabled, but I may assume that something around this is causing the performance degradation. But unfortunately I cannot step forward right now. Regards, Kojedzinszky Richard On Wed, 27 Nov 2013, Tom Evans wrote: > 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 >
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