Date: Fri, 17 Oct 2014 09:10:48 +0100 From: krad <kraduk@gmail.com> To: Don Lewis <truckman@freebsd.org> Cc: freebsd-stable <freebsd-stable@freebsd.org>, Steven Hartland <killing@multiplay.co.uk>, fullermd@over-yonder.net Subject: Re: getting to 4K disk blocks in ZFS Message-ID: <CALfReyfazoZ-Xjwnb=iMmrhU30CXNyMVjdOr=VygzcwjQKEo8Q@mail.gmail.com> In-Reply-To: <201410132047.s9DKlGxD030176@gw.catspoiler.org> References: <43D94A22FBD2477FBBDEFF16C0088DDA@multiplay.co.uk> <201410132047.s9DKlGxD030176@gw.catspoiler.org>
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your also forgetting you can enable compression, which on mail files will give you a large ratio On 13 October 2014 21:47, Don Lewis <truckman@freebsd.org> wrote: > On 13 Oct, Steven Hartland wrote: > > ----- 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/ > > This is a timely subject. I'm planning on moving my Cyrus imap mail > spool from a 4K/1K UFS filesystem to a three drive raidz1. It looks > like the UFS fragmentation overhead is about 2.4%. ZFS ashift=12 > increases that to about 17%. Combine that with raidz and now the > overhead is about 40%. Ouch! > > _______________________________________________ > freebsd-stable@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-stable > To unsubscribe, send any mail to "freebsd-stable-unsubscribe@freebsd.org" >
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