From owner-freebsd-fs@freebsd.org Wed Aug 19 16:10:39 2015 Return-Path: Delivered-To: freebsd-fs@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 514499BEA9B for ; Wed, 19 Aug 2015 16:10:39 +0000 (UTC) (envelope-from paul@pk1048.com) Received: from cpanel61.fastdnsservers.com (server61.fastdnsservers.com [216.51.232.61]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 2F55CC2E for ; Wed, 19 Aug 2015 16:10:38 +0000 (UTC) (envelope-from paul@pk1048.com) Received: from mail.thecreativeadvantage.com ([96.236.20.34]:63449 helo=mbp-1.thecreativeadvantage.com) by cpanel61.fastdnsservers.com with esmtpsa (TLSv1:AES128-SHA:128) (Exim 4.85) (envelope-from ) id 1ZS5wj-001cVZ-Le; Wed, 19 Aug 2015 11:10:37 -0500 Subject: Re: Optimizing performance with SLOG/L2ARC Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) Content-Type: text/plain; charset=windows-1252 From: PK1048 In-Reply-To: Date: Wed, 19 Aug 2015 12:10:39 -0400 Cc: javocado , "Schweiss, Chip" Content-Transfer-Encoding: quoted-printable Message-Id: <3FE10173-656C-4744-AB2D-32148A34CB46@pk1048.com> References: <023F881D-CCC5-4FCA-B09D-EB92C3BFBC03@pk1048.com> To: FreeBSD Filesystems X-Mailer: Apple Mail (2.1878.6) X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - cpanel61.fastdnsservers.com X-AntiAbuse: Original Domain - freebsd.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - pk1048.com X-Get-Message-Sender-Via: cpanel61.fastdnsservers.com: authenticated_id: info@pk1048.com X-Source: X-Source-Args: X-Source-Dir: X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 19 Aug 2015 16:10:39 -0000 On Aug 19, 2015, at 12:02, Schweiss, Chip wrote: > On Wed, Aug 19, 2015 at 10:29 AM, PK1048 wrote: >=20 >>=20 >> Please note that, depending on your workload, an SSD may _not_ be any >> faster than a HDD. I am in the process of rebuilding a file server = that >> exhibited poor NFS SYNC write performance. Yet it had a mirrored pair = of >> SSDs. Unfortunately, those SSDs had _worse_ write performance than an = HDD >> for small (4 KB) writes. Based on recommendations from the OpenZFS = list I >> have a pair of Intel 3710 SSDs coming in to try, they are supposed to = have >> much better write performance (at all block sizes) and much better >> reliability long term (10x full disk writes per day for 5 years). = I=92ll know >> more once they arrive and I can test with them. >>=20 >=20 > Pure SSD pools still need a log device. Sorry I was unclear, I was NOT suggesting a pure SSD pool. > ZFS doesn't play well with the > ZIL on the pool with SSDs. Even an SSD of the same type as the pool > devices as the log device will fix the latency problem and throughput > problems. If your load is sync writes then you decidedly want a LOG device, even = if it is the same type as the devices in the pool. For the reasons = others have posted. > It seems counter-intuitive but a very real problem, there is a long = thread > about this on the Illumos ZFS list. If you don't believe it, turn off = sync > on your SSD pool and performance will skyrocket. But remember to turn it back on after you test so that you don=92t break = posix sync behavior and raise the possibility of loosing writes in = flight. I am horrified at the number of posts on the Internet that tell = you to simply disable sync to fix sync performance issues (VM images = accessed via NFS being a very common one).