From owner-freebsd-stable@FreeBSD.ORG Fri Dec 6 17:23:53 2013 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id 1100BF7E for ; Fri, 6 Dec 2013 17:23:53 +0000 (UTC) Received: from out2-smtp.messagingengine.com (out2-smtp.messagingengine.com [66.111.4.26]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.freebsd.org (Postfix) with ESMTPS id D42FD1071 for ; Fri, 6 Dec 2013 17:23:52 +0000 (UTC) Received: from compute2.internal (compute2.nyi.mail.srv.osa [10.202.2.42]) by gateway1.nyi.mail.srv.osa (Postfix) with ESMTP id 142D2210B4 for ; Fri, 6 Dec 2013 12:23:33 -0500 (EST) Received: from web3 ([10.202.2.213]) by compute2.internal (MEProxy); Fri, 06 Dec 2013 12:23:33 -0500 DKIM-Signature: v=1; a=rsa-sha1; c=relaxed/relaxed; d= messagingengine.com; h=message-id:from:to:mime-version :content-transfer-encoding:content-type:in-reply-to:references :subject:date; s=smtpout; bh=YyohggvHlghh2IqEqmjuHZA4xxg=; b=Pgf dpNHNi7cfe5Sgf0bNVw5ldbAc50T1SkFRF9wlQh8gMW+w0H/Pr/+TTPWGT33zgHh buUJT7uFNwxr0cLs6H8bEIXEm99G6f7W3J85YzLpYpRng+Q4ktJ7W1VizCXImICJ ns+O6SR8f9ox4M/qF+Qnso8Gl2l+cLByu/r6I6PU= Received: by web3.nyi.mail.srv.osa (Postfix, from userid 99) id E2EEF180A64; Fri, 6 Dec 2013 12:23:32 -0500 (EST) Message-Id: <1386350612.24515.56413717.7535920E@webmail.messagingengine.com> X-Sasl-Enc: IndblUD9/+7zSDuvtT64QASsE8ejsNsP7EZ3rcez1JVi 1386350612 From: Mark Felder To: freebsd-stable@freebsd.org MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="ISO-8859-1" X-Mailer: MessagingEngine.com Webmail Interface - ajax-c99dcdd8 In-Reply-To: References: Subject: Re: Does FreeBSD's ZFS reserve 1/64 of the capacity for COW? Date: Fri, 06 Dec 2013 11:23:32 -0600 X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.17 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 06 Dec 2013 17:23:53 -0000 On Fri, Dec 6, 2013, at 6:46, Trond Endrest=F8l wrote: > Hi, >=20 > Today I came across "Becoming a ZFS Ninja Part 1"=20 > http://www.youtube.com/watch?v=3DtPsV_8k-aVU featuring Ben Rockwood who=20 > stated that ZFS reserves 1/64 of the capacity for COW safe-guarding.=20 > Fast forward to 00:49:44. Thus, one should take this fact into account=20 > when planning the storage capacity of your (larger) zpools. >=20 > Does FreeBSD's ZFS also reserve 1/64 of the capacity for COW? >=20 > If it's true, then I guess this should be noted in zpool(8) and in the=20 > Handbook. >=20 Well, the rule-of-thumb / urban legend tends to be "don't let your zpool go over ~80% or you'll have severe performance issues" so I'm not sure that statement is accurate or COW wouldn't be so painful when your pool is over ~80%. I could be wrong though; I often am :-)