Date: Mon, 13 Jun 2011 02:48:03 -0700 From: Jeremy Chadwick <freebsd@jdc.parodius.com> To: Steven Hartland <killing@multiplay.co.uk> Cc: freebsd-fs@FreeBSD.ORG Subject: Re: Impossible compression ratio on ZFS Message-ID: <20110613094803.GA10290@icarus.home.lan> In-Reply-To: <F21D6DCDBA494B4A9FDF20A13BC4947A@multiplay.co.uk> References: <F21D6DCDBA494B4A9FDF20A13BC4947A@multiplay.co.uk>
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On Mon, Jun 13, 2011 at 10:13:33AM +0100, Steven Hartland wrote: > I've just done an optimisation of a mysql table which is located > on a compressed zfs partition and spotted that the size reported > by du is impossibly small for the file:- > > du -h detail* > 1.5K detail.frm > 7.5K detail.ibd > > ls -l detail* > -rw-rw---- 1 mysql mysql 8660 Jun 13 10:00 detail.frm > -rw-rw---- 1 mysql mysql 650117120 Jun 13 10:04 detail.ibd > > The table format for those interested is 3 int's, 3 indexes and > contains 8million rows. > > I highly doubt that my 620MB table is taking up just 7.5K on disk > any ideas? Well-known "quirk"; welcome to ZFS. :-) The following article is long, but if you grab a coffee and read it in full, it'll shed some light on the ordeal: http://www.cuddletech.com/blog/pivot/entry.php?id=983 There's also this: http://blog.buttermountain.co.uk/2008/05/10/zfs-compression-when-du-and-ls-appear-to-disagree/ This is one of the many reasons I do not use ZFS compression. Not spreading FUD, just saying stuff like this throws users for a loop, case in point. -- | Jeremy Chadwick jdc@parodius.com | | Parodius Networking http://www.parodius.com/ | | UNIX Systems Administrator Mountain View, CA, US | | Making life hard for others since 1977. PGP 4BD6C0CB |
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