From owner-freebsd-questions@freebsd.org Thu Feb 14 14:48:54 2019 Return-Path: Delivered-To: freebsd-questions@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 9F0CE14D6B67 for ; Thu, 14 Feb 2019 14:48:54 +0000 (UTC) (envelope-from kraduk@gmail.com) Received: from mail-it1-x12f.google.com (mail-it1-x12f.google.com [IPv6:2607:f8b0:4864:20::12f]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 52269745CC for ; Thu, 14 Feb 2019 14:48:53 +0000 (UTC) (envelope-from kraduk@gmail.com) Received: by mail-it1-x12f.google.com with SMTP id z131so5160657itf.5 for ; Thu, 14 Feb 2019 06:48:53 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=3JQ3mX+kKzCZae2aWFdxNw2/vjKlRzLrFwPW5nymyWw=; b=BQF2lJe6ManDBsPJCXBv2YkzoE5NdNBO6+9NnsSqmYNnm8J2YTEuIEpL9srS6k067L t3NmHQIOZ/9wgWevs7YNmI3B5Az8xeNxtP+IqFVsRRXehx2tciCmSiJev7lS3yhix070 hxD8c9GtI8BMRjkS8DAyJt3wxt/Mbd4m0gFOMepZAqFpS9DUbw7AcwObMQlfjs1izkqA URisLM1DuiRh2NnjacifiKu5fBJSwTcmMOQmsFCMJXnCX2OlBE6XOYVj+5fajbc/8rLj 7hsQPXGrNUYoZ/6cPQCpOCXLW/+gcpDn9XXRlSDuG1joGRgk+SQbjezoA/xt8EPHEBqR n4hg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=3JQ3mX+kKzCZae2aWFdxNw2/vjKlRzLrFwPW5nymyWw=; b=OUepWhyz+vKYWww0mbcaTjnkyt6SETZJvG3SSrDhXYoO2Fypi1pNTBsscThL83LR9T DU+i3uGQFHMZgXG0WGlliZP0upnIukI+zmbExks+BplXDJub5dA1p+nkL1yUAbmMvrk1 9Sc+8Oj+/IoaUJcS+lqJjYNaYV6TJGXWNHV5hzadyviaBJuE5mb41SGSoD3DEoNLv5HB XRnRnFx+i22wlNj+Q2Hp//tNZnMxFQjcaORzlcbhch2pIbEqlEGb2HM/E+30egwn/3BN +a4sRSsZDv+BBirw0cx00H9A/WTMSt/pMb5y75W7W8XgSrheTwSm01K1fOBZ3dP68nxE vk0A== X-Gm-Message-State: AHQUAuYVIMkSqjbm9wtBasCCDwkPBTA/nAJh2B1NGg+NpDV048QYO9Di 4YMvR4Zol1/DufR6u9K4mRzYxnT4mLnbhExVLQTFXA== X-Google-Smtp-Source: AHgI3IY25nG1IN90V5J1zw35Sgyy6KEfjBkJj4GfIVGHJYkk5Mpqlpqglo8z44wwNms4WXh3SXAlrj5zzoEphQjTeZ4= X-Received: by 2002:a02:8303:: with SMTP id v3mr1764925jag.51.1550155732614; Thu, 14 Feb 2019 06:48:52 -0800 (PST) MIME-Version: 1.0 References: <20190213171142.33b7c430c5ec256b1cbafa42@sohara.org> In-Reply-To: <20190213171142.33b7c430c5ec256b1cbafa42@sohara.org> From: krad Date: Thu, 14 Feb 2019 14:48:41 +0000 Message-ID: Subject: Re: ZFS and a spare SSD: ZIL or L2ARC? To: "Steve O'Hara-Smith" Cc: FreeBSD Questions X-Rspamd-Queue-Id: 52269745CC X-Spamd-Bar: ----- Authentication-Results: mx1.freebsd.org; dkim=pass header.d=gmail.com header.s=20161025 header.b=BQF2lJe6; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (mx1.freebsd.org: domain of kraduk@gmail.com designates 2607:f8b0:4864:20::12f as permitted sender) smtp.mailfrom=kraduk@gmail.com X-Spamd-Result: default: False [-5.69 / 15.00]; R_SPF_ALLOW(-0.20)[+ip6:2607:f8b0:4000::/36]; FREEMAIL_FROM(0.00)[gmail.com]; TO_DN_ALL(0.00)[]; MX_GOOD(-0.01)[cached: alt3.gmail-smtp-in.l.google.com]; DKIM_TRACE(0.00)[gmail.com:+]; RCPT_COUNT_TWO(0.00)[2]; NEURAL_HAM_SHORT(-0.94)[-0.937,0]; DMARC_POLICY_ALLOW(-0.50)[gmail.com,none]; FROM_EQ_ENVFROM(0.00)[]; RCVD_TLS_LAST(0.00)[]; SUBJECT_ENDS_QUESTION(1.00)[]; FREEMAIL_ENVFROM(0.00)[gmail.com]; ASN(0.00)[asn:15169, ipnet:2607:f8b0::/32, country:US]; DWL_DNSWL_NONE(0.00)[gmail.com.dwl.dnswl.org : 127.0.5.0]; ARC_NA(0.00)[]; NEURAL_HAM_MEDIUM(-1.00)[-1.000,0]; R_DKIM_ALLOW(-0.20)[gmail.com:s=20161025]; FROM_HAS_DN(0.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000,0]; MIME_GOOD(-0.10)[multipart/alternative,text/plain]; PREVIOUSLY_DELIVERED(0.00)[freebsd-questions@freebsd.org]; TO_MATCH_ENVRCPT_SOME(0.00)[]; RCVD_IN_DNSWL_NONE(0.00)[f.2.1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.2.0.0.4.6.8.4.0.b.8.f.7.0.6.2.list.dnswl.org : 127.0.5.0]; MIME_TRACE(0.00)[0:+,1:+]; RCVD_COUNT_TWO(0.00)[2]; IP_SCORE(-2.74)[ip: (-9.11), ipnet: 2607:f8b0::/32(-2.55), asn: 15169(-1.98), country: US(-0.07)] Content-Type: text/plain; charset="UTF-8" X-Content-Filtered-By: Mailman/MimeDel 2.1.29 X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 14 Feb 2019 14:48:54 -0000 You need to be careful with L2ARC as under certain conditions it can actually degrade performance. This is down to you needing a data structure in ram to manage the l2arc. This comes at the expense of ARC. However this is more of an edge case when you are adding huge amounts of L2ARC compared to system ram, but important in the enterprise world. >From your described workload ZiL might be better suited as databases and virtualisation often cause lots of sync writes. This is where Zil can help. However the picture is never simple. If you are going to have a zil you really want it mirrored, as like others have said its critical if it fails. Your SSD also needs to have good write endurance. You can achieve this by either spending loads and getting a high quality drive or over capacitying something cheaper. (as bigger drives have a higher lifetime writes). However you do this you are relying on the wear levelling working correctly. Another thing to consider is again a separate ZiL can hurt performance, depending on workloads and the configuration of the main pool vs the ssd/nve used. A large zpool can have a higher write throughput than a single puny ssd so unless you are heavily io contended you would hurt performance in this scenario. Sorry to paint a complicated picture but like most things there is no right or wrong, just choices and balancing of risks. On Wed, 13 Feb 2019 at 17:15, Steve O'Hara-Smith wrote: > On Wed, 13 Feb 2019 18:02:51 +0100 > Andrea Venturoli wrote: > > > Now I've just got hold of a spare SSD and, although the box performance > > is adequate, I'd like to see if it can boost it. > > Should I configure it as L2ARC? ZIL? Both? > > In my experience L2ARC tends to run full and ZIL uses almost none > of the space allocated. But then my workload is read heavy - for a write > heavy workload ZIL is probably more beneficial. > > -- > Steve O'Hara-Smith > _______________________________________________ > freebsd-questions@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-questions > To unsubscribe, send any mail to " > freebsd-questions-unsubscribe@freebsd.org" >