From owner-freebsd-fs@freebsd.org Wed Aug 19 16:06:12 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 F39F29BE8B2 for ; Wed, 19 Aug 2015 16:06:12 +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 D308386D for ; Wed, 19 Aug 2015 16:06:12 +0000 (UTC) (envelope-from paul@pk1048.com) Received: from mail.thecreativeadvantage.com ([96.236.20.34]:63422 helo=mbp-1.thecreativeadvantage.com) by cpanel61.fastdnsservers.com with esmtpsa (TLSv1:AES128-SHA:128) (Exim 4.85) (envelope-from ) id 1ZS5sR-001bvZ-T3; Wed, 19 Aug 2015 11:06:11 -0500 Content-Type: text/plain; charset=windows-1252 Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) Subject: Re: Optimizing performance with SLOG/L2ARC From: PK1048 In-Reply-To: <20150819154650.GA78333@neutralgood.org> Date: Wed, 19 Aug 2015 12:06:13 -0400 Content-Transfer-Encoding: quoted-printable Message-Id: <3C6E3C03-9A64-4CEC-8238-2A73F4EE26D1@pk1048.com> References: <023F881D-CCC5-4FCA-B09D-EB92C3BFBC03@pk1048.com> <20150819154650.GA78333@neutralgood.org> 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 16:06:13 -0000 On Aug 19, 2015, at 11:46, kpneal@pobox.com wrote: > On Wed, Aug 19, 2015 at 11:29:44AM -0400, PK1048 wrote: >> Someone commented on the size of the ZIL/SLOG=85 it needs to hold all = of the write data that arrives between TXG commits, which happen at = least every 5 seconds (it used to be 30 seconds, but that scared too = many people :-). SU a sync write arrives and it _must_ be committed to = permanent storage, so ZFS writes it to the ZFS Intent Log (ZIL) which = may or may not be a separate device (vdev). When the TXG that contains = that data is committed to the pool itself the data can be flushed from = the ZIL. If your source of sync writes is network shares, and you have a = 1 Gbps link, then your maximum ZIL will be 5 seconds x 1 Gbps or 5 = Gigabits. >=20 > That was me. By your figures 5 Gigabits is small compared to the size = of > SSD these days. If the SLOG ends up being that important to = performance > then it may make sense to buy small, excellent quality SSD. Exactly, unless your sync write data is coming from a _local_ = application or you have multiple 10 G ethernet connections :-) When I asked about SSD recommendations and sizing over on the OpenZFS = list, the consensus was that a 32 GB log device was probably big enough = for any rational load. I ordered 200 GB 3710=92s =85 sometimes = performance also scales with capacity, so be careful buying the smallest = SSD that fits the strict size needs. I will partition them and use some = for LOG and some for L2ARC (if I need it). I know this is not = recommended, but if it works, why not (and I do understand the = limitations of such a configuration). I only have 24 GB RAM in this box = and can probably benefit from some L2ARC. > I believe they even make PCIe battery-backed up RAM for this use. I = have > no idea about the price, though. Probably a lot. But maybe "a lot" = isn't > much depending on the value of the service provided by the machine. I have seen the RAM based battery-backed-up drives, and some are not = even ludicrous in terms of price, but I did not see any with FreeBSD = driver support. Since they are generally PCIe based (for speed), drives = are needed.