From owner-freebsd-scsi@FreeBSD.ORG Thu Nov 28 01:02:39 2013 Return-Path: Delivered-To: freebsd-scsi@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id E927AD9C for ; Thu, 28 Nov 2013 01:02:38 +0000 (UTC) Received: from mail3.transactionware.com (mail3.transactionware.com [202.68.173.211]) by mx1.freebsd.org (Postfix) with SMTP id 509B0A17 for ; Thu, 28 Nov 2013 01:02:36 +0000 (UTC) Received: (qmail 16359 invoked by uid 907); 28 Nov 2013 00:55:53 -0000 Received: from eth222.nsw.adsl.internode.on.net (HELO [192.168.1.32]) (150.101.196.221) (smtp-auth username janm, mechanism plain) by mail3.transactionware.com (qpsmtpd/0.84) with (AES128-SHA encrypted) ESMTPSA; Thu, 28 Nov 2013 11:55:53 +1100 Content-Type: text/plain; charset=iso-8859-1 Mime-Version: 1.0 (Mac OS X Mail 7.0 \(1812\)) Subject: Re: ssd for zfs From: Jan Mikkelsen In-Reply-To: <0b12c19b8832c72369ff7244d7231846@cflinux.hu> Date: Thu, 28 Nov 2013 11:55:51 +1100 Content-Transfer-Encoding: quoted-printable Message-Id: References: <0b12c19b8832c72369ff7244d7231846@cflinux.hu> To: krichy@cflinux.hu X-Mailer: Apple Mail (2.1812) Cc: freebsd-scsi@freebsd.org X-BeenThere: freebsd-scsi@freebsd.org X-Mailman-Version: 2.1.16 Precedence: list List-Id: SCSI subsystem List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 28 Nov 2013 01:02:39 -0000 Hi, Using the drive write cache seems like a really bad idea for a ZIL. The purpose of a ZIL is to keep a log of actions for recovery after a = system crash. The drive write cache lets the drive lie to the operating = system about whether or not a write has been made durable. If you have a = power failure while you have 1400 writes outstanding to the drive you = might find that you have data loss on restart. For a ZIL you are best off with a drive that has a supercapacitor to = ensure all outstanding writes can be completed on power loss. For = example, the Intel S3700 series. Performance on your zpool is probably limited by the number of vdevs you = have. More vdevs give more I/O parallelism. If you only have one vdev = you will be limited to single drive throughput. Depending on the number = of drives you have and what you need, you will either need a bunch of = mirrored vdevs or a bunch of raidz2 vdevs (if you have enough drives). I made this mistake early on, thinking a raidz2 vdev alone would give = parallelism. You need multiple vdevs. Regards, Jan Mikkelsen janm@transactionware.com On 28 Nov 2013, at 1:14 am, krichy@cflinux.hu wrote: >=20 >=20 > -------- Eredeti =FCzenet -------- > T=E1rgy: Re: ssd for zfs > D=E1tum: 2013-11-27 14:07 > Felad=F3: Richard Kojedzinszky > C=EDmzett: Tom Evans > M=E1solat: FreeBSD FS >=20 > Dear FS devs, >=20 > 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. >=20 > Regards, >=20 > Kojedzinszky Richard >=20 > On Wed, 27 Nov 2013, Tom Evans wrote: >=20 >> On Wed, Nov 27, 2013 at 8:51 AM, Richard Kojedzinszky = 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 > _______________________________________________ > freebsd-scsi@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-scsi > To unsubscribe, send any mail to = "freebsd-scsi-unsubscribe@freebsd.org"