Date: Mon, 9 Dec 2013 08:33:11 -0700 From: Warner Losh <imp@bsdimp.com> To: =?iso-8859-1?Q?Trond_Endrest=F8l?= <Trond.Endrestol@fagskolen.gjovik.no> Cc: freebsd-stable@freebsd.org Subject: Re: Does FreeBSD's ZFS reserve 1/64 of the capacity for COW? Message-ID: <01D335F5-1B57-4B3E-BE78-38794F65B7A9@bsdimp.com> In-Reply-To: <alpine.BSF.2.00.1312090813270.75198@mail.fig.ol.no> References: <alpine.BSF.2.00.1312061325420.75198@mail.fig.ol.no> <1386350612.24515.56413717.7535920E@webmail.messagingengine.com> <alpine.BSF.2.00.1312090813270.75198@mail.fig.ol.no>
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On Dec 9, 2013, at 12:15 AM, Trond Endrestøl wrote: > On Fri, 6 Dec 2013 11:23-0600, Mark Felder wrote: > >> >> >> On Fri, Dec 6, 2013, at 6:46, Trond Endrestøl wrote: >>> Hi, >>> >>> Today I came across "Becoming a ZFS Ninja Part 1" >>> http://www.youtube.com/watch?v=tPsV_8k-aVU featuring Ben Rockwood who >>> stated that ZFS reserves 1/64 of the capacity for COW safe-guarding. >>> Fast forward to 00:49:44. Thus, one should take this fact into account >>> when planning the storage capacity of your (larger) zpools. >>> >>> Does FreeBSD's ZFS also reserve 1/64 of the capacity for COW? >>> >>> If it's true, then I guess this should be noted in zpool(8) and in the >>> Handbook. >>> >> >> 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 :-) > > As it turns out, you're in good company, I'm also wrong far too often. I have a zpool that I share between development (/usr/src) and videos (tivo backups). When it gets over 90% full, I start to see buildworld or svn operations slow way down... Warner
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