Date: Mon, 9 Dec 2013 08:15:05 +0100 (CET) From: =?ISO-8859-1?Q?Trond_Endrest=F8l?= <Trond.Endrestol@fagskolen.gjovik.no> To: Freddie Cash <fjwcash@gmail.com> Cc: FreeBSD stable <freebsd-stable@freebsd.org> Subject: Re: Does FreeBSD's ZFS reserve 1/64 of the capacity for COW? Message-ID: <alpine.BSF.2.00.1312090808000.75198@mail.fig.ol.no> In-Reply-To: <CAOjFWZ6fd0dGCgcbvV6T=nw=VFUfdcRCu4DcMiQxZxyt4E=vrg@mail.gmail.com> References: <alpine.BSF.2.00.1312061325420.75198@mail.fig.ol.no> <CAOjFWZ6fd0dGCgcbvV6T=nw=VFUfdcRCu4DcMiQxZxyt4E=vrg@mail.gmail.com>
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On Fri, 6 Dec 2013 08:47-0800, Freddie Cash wrote: > On Fri, Dec 6, 2013 at 4:46 AM, Trond Endrestøl < > Trond.Endrestol@fagskolen.gjovik.no> 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. > > > > Any comments or insights? > > Do you think I should file a PR? > > > > Have a nice weekend! ;-) > > > > Based on the experience I went through a week or so ago, I would have to > say, no. (Unless this is an unrelated issue.) > > I filled a 75 TB pool 100% full, 0 bytes left. Was unable to delete files, > was unable to "cp /dev/null" files, was unable to truncate files.?? Mostly > due to snapshots and "deleting" a file actually marks the blocks as part of > the previous snapshot and updates a bunch of metadata. And, was unable to > destroy any snapshots as there was 0 space to write out metadata. > > Thankfully, I had 1 ZFS filesystem without any snapshots, and I was able to > successfully delete files from that dataset. Once a few MB of free space > was made available, then I was able to start deleting snapshots > > ?I now have a dataset on each ZFS pool called "do-not-delete" with a 1 GB > reservation (and no snapshots). This way, if the pool ever gets filled to > 100% (and it did a few days later), it's a simple matter to "create" free > space: > # zfs set reservation=512M storage/do-not-delete > ? > Then delete some snapshots, and set the reservation back to 1 GB. > > I've now hit the 100% full issue 3 times. Twice, the do-not-delete > reservation saved me. That's a handy tip. Thanks. -- +-------------------------------+------------------------------------+ | Vennlig hilsen, | Best regards, | | Trond Endrestøl, | Trond Endrestøl, | | IT-ansvarlig, | System administrator, | | Fagskolen Innlandet, | Gjøvik Technical College, Norway, | | tlf. mob. 952 62 567, | Cellular...: +47 952 62 567, | | sentralbord 61 14 54 00. | Switchboard: +47 61 14 54 00. | +-------------------------------+------------------------------------+
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