Date: Thu, 7 Dec 2000 12:56:03 -0800 (PST) From: Matt Dillon <dillon@earth.backplane.com> To: Warner Losh <imp@village.org> Cc: Poul-Henning Kamp <phk@critter.freebsd.dk>, A G F Keahan <ak@freenet.co.uk>, freebsd-hackers@FreeBSD.ORG Subject: Re: Optimal UFS parameters Message-ID: <200012072056.eB7Ku3112378@earth.backplane.com> References: <200012070821.eB78LeQ07926@earth.backplane.com> <58936.976176750@critter> <200012072009.NAA06489@harmony.village.org>
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:In message <200012070821.eB78LeQ07926@earth.backplane.com> Matt Dillon writes:
:: : -b 16384 -f 4096 -c 159
:: I think Bruce swears by 4K (page-sized) fragments. Not a bad
:: way to go. I use 2K because I (and others) put in so much hard work
:: to fix all the little niggling bugs in the VM system related to partial
:: page validation and, damn it, I intend to use those features!
:
:At the other end of the spectrum, 32M [sic] and 64M [sic] disks work
:well with
: -b 4096 -f 512 -c 10
:
:But I tend to do what phk has done with the large -c flags on my
:insanely-sized, rediculously-cheap XXG IDE drives.
:
:Warner
Well, too-large a C/G will result in greater file fragmentation,
because FFS can't manage the file layouts in the cylinder groups
as well. The default of 16 is definitely too little. 100+ is probably
too much. Something in the middle will be about right.
The fragmentation value returned by fsck would be an interesting number
to publish. 'fsck -n /dev/...' on an idle fs (you don't have to unmount
it). Anything over 3% fragmentation is a problem. Something like
/usr will typically be in the 1-3% range. A large partition that is
still half empty should be in the 0.0-0.5% range.
A combination of a larger C/G (meaning fewer groups on the disk)
and fewer inodes (a higher -i value) will dramatically decrease fsck
times. After a certain point, though, continuing to increase C/G will not
effect the fsck times.
-Matt
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