Date: Mon, 13 Jun 2011 11:57:22 +0100 From: "Steven Hartland" <killing@multiplay.co.uk> To: "Jeremy Chadwick" <freebsd@jdc.parodius.com> Cc: freebsd-fs@FreeBSD.ORG Subject: Re: Impossible compression ratio on ZFS Message-ID: <4E09C82B45BA46019281930B2EB13AC1@multiplay.co.uk> References: <F21D6DCDBA494B4A9FDF20A13BC4947A@multiplay.co.uk> <20110613094803.GA10290@icarus.home.lan>
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----- Original Message ----- From: "Jeremy Chadwick" <freebsd@jdc.parodius.com> > 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. I think your miss-understanding my question, its not the fact that its showing different sizes from du and ls, that's 100% expected but clearly 8million rows of 3 int's can't possibly compress down to 7.5K. Having just looked back at the machine, an hour later, the values now seem correct with du showing:- 278M detail.ibd I checked this several times, over what had to be 10mins or more even did a flush tables to ensure everything had been written out as far as mysql was concerned. So it seems that zfs was still processing the file for a good amount of time, and during that time was showing incorrect disk usage for said file. I'm wondering if the data is some how being processed in l2 arc or something? For reference we're running 8.2-RELEASE, on an areca backed raid6 with two ssd drives in l2 arc. zpool status pool: tank state: ONLINE scrub: none requested config: NAME STATE READ WRITE CKSUM tank ONLINE 0 0 0 da0p3 ONLINE 0 0 0 cache ada0 ONLINE 0 0 0 ada1 ONLINE 0 0 0 errors: No known data errors Obviously everything seems to have caught up and is now showing real stats but confused as to why it would take quite so long to display the real usage via du. Regards Steve ================================================ This e.mail is private and confidential between Multiplay (UK) Ltd. and the person or entity to whom it is addressed. In the event of misdirection, the recipient is prohibited from using, copying, printing or otherwise disseminating it or any information contained in it. In the event of misdirection, illegible or incomplete transmission please telephone +44 845 868 1337 or return the E.mail to postmaster@multiplay.co.uk.
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