Date: Fri, 06 Dec 2013 11:23:32 -0600 From: Mark Felder <feld@FreeBSD.org> To: freebsd-stable@freebsd.org Subject: Re: Does FreeBSD's ZFS reserve 1/64 of the capacity for COW? Message-ID: <1386350612.24515.56413717.7535920E@webmail.messagingengine.com> In-Reply-To: <alpine.BSF.2.00.1312061325420.75198@mail.fig.ol.no> References: <alpine.BSF.2.00.1312061325420.75198@mail.fig.ol.no>
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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 :-)
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