Date: Wed, 27 Nov 2013 17:25:47 +0100 From: krichy@cflinux.hu To: freebsd-questions@freebsd.org Subject: Fwd: Re: ssd for zfs Message-ID: <3ed476ffcc57b303380c3d6c2b293381@cflinux.hu>
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Dear users, I am facing with a problem that my new SSD seems to behave on freebsd as its write cache had been turned off. And I could not make it enabled. Under linux, if I attach it to a ZFS pool as a log device, the pool can reach around 1400 write IOPS, but the same under freebsd is just only 100 IOPS. Under linux I could disable the write cache, when the performance also dropped to 100 IOPS. The device itself handles the write cache well, so I would like to use it with that enabled. Any advice, where to go? What to debug? The SSD is an STEC MACH16 SLC 50GB SSD. FreeBSD is a 9.2-STABLE, up-to-date. Thanks in advance, -------- Eredeti üzenet -------- Tárgy: Fwd: Re: ssd for zfs Dátum: 2013-11-27 15:14 Feladó: krichy@cflinux.hu Címzett: freebsd-scsi@freebsd.org -------- Eredeti üzenet -------- Tárgy: Re: ssd for zfs Dátum: 2013-11-27 14:07 Feladó: Richard Kojedzinszky <krichy@cflinux.hu> Címzett: Tom Evans <tevans.uk@googlemail.com> Másolat: FreeBSD FS <freebsd-fs@freebsd.org> 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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