From owner-freebsd-fs@FreeBSD.ORG Wed Nov 27 13:07:05 2013 Return-Path: Delivered-To: freebsd-fs@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 61F5597C for ; Wed, 27 Nov 2013 13:07:05 +0000 (UTC) Received: from pi.nmdps.net (pi.nmdps.net [IPv6:2a01:be00:10:201:0:80:0:1]) by mx1.freebsd.org (Postfix) with ESMTP id 250FF2EC7 for ; Wed, 27 Nov 2013 13:07:05 +0000 (UTC) Received: from pi.nmdps.net (pi.nmdps.net [109.61.102.5]) (Authenticated sender: krichy@cflinux.hu) by pi.nmdps.net (Postfix) with ESMTPSA id 3BC831255; Wed, 27 Nov 2013 14:07:04 +0100 (CET) Date: Wed, 27 Nov 2013 14:07:01 +0100 (CET) From: Richard Kojedzinszky X-X-Sender: krichy@pi.nmdps.net To: Tom Evans Subject: Re: ssd for zfs In-Reply-To: Message-ID: References: User-Agent: Alpine 2.00 (BSF 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Cc: FreeBSD FS X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.16 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 27 Nov 2013 13:07:05 -0000 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 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 >