Date: Mon, 10 Aug 2015 09:20:35 -0400 From: PK1048 <paul@pk1048.com> To: FreeBSD Filesystems <freebsd-fs@freebsd.org> Subject: Re: Urgently need some help solving lost space due to snapshots during receive op Message-ID: <43B00232-46B7-4B96-B80C-D0111C6D8DA2@pk1048.com> In-Reply-To: <55C863DE.3000200@digiware.nl> References: <55C82BCD.2050404@herveybayaustralia.com.au> <55C863DE.3000200@digiware.nl>
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On Aug 10, 2015, at 4:42, Willem Jan Withagen <wjw@digiware.nl> wrote: > Last number I remember as sensible maximum fill level is around 70%. > If you go over it, your system is going to be busy with ZFS = bookkeeping > instead of data storage. Fortunately or not, that number is _very_ dependent on your specific = data and how it is loaded. If it is static data, loaded once and not = modified, you can run a much higher % Used, for lots of changes on an = ongoing basis you need much more free space. The issue is that since ZFS = is Copy on Write, every write (even a modification to an existing file = or disk block) needs to find space. ZFS tries to reduce fragmentation. = As the zpool gets more and more full it takes longer and longer to find = the best possible location to put the new write. It also becomes harder = and harder to find contiguous blocks to put the new write into. The = existence of snapshots makes this problem even worse, as previously = written data is not cleared until the snapshot is destroyed.
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