Date: Mon, 13 Oct 2014 20:22:31 +0100 From: "Steven Hartland" <killing@multiplay.co.uk> To: "Matthew D. Fuller" <fullermd@over-yonder.net>, "freebsd-stable" <freebsd-stable@freebsd.org> Subject: Re: getting to 4K disk blocks in ZFS Message-ID: <43D94A22FBD2477FBBDEFF16C0088DDA@multiplay.co.uk> References: <540FF3C4.6010305@ish.com.au> <54100258.2000505@freebsd.org> <5410F0B4.9040808@ish.com.au> <A0A549F7A4094F519A3660697AB4983F@multiplay.co.uk> <543C1E7B.4090204@bluerosetech.com> <20141013191903.GR2161@over-yonder.net>
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----- Original Message ----- From: "Matthew D. Fuller" <fullermd@over-yonder.net> > On Mon, Oct 13, 2014 at 11:48:27AM -0700 I heard the voice of > Darren Pilgrim, and lo! it spake thus: >> >> If the default is 4k and (for the limited time they're still common) >> you use true 512b disks, you can waste space. Sure, but how much >> space? > > The median file in /usr/ports is 408 bytes. Over 90% of the files are > under 2k, which means the wastage for them is over 100% (before > counting what gain compression might get). A little offhand mathery > says it's about 78% extra overhead on the whole. > > And that includes the almost hundred megs (over 22% of the total size > of the FS) for the INDEX.db, plus the ~90 megs of the flat INDEX files > (another 20%). If you pull those out, the overhead is 130%. > > > (To be sure, relatively few people have ports trees eating most of > their space, but still; it's pretty pathological. I for one did > decide some years back to always force 4k on any new FSen to make > future life simpler, accepting the bloat, but it's there.) And thats before you add the overhead if your running RAIDZ... A good read on this is http://blog.delphix.com/matt/2014/06/06/zfs-stripe-width/ Regards Steve
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