Date: Wed, 27 Oct 1999 23:02:01 -0400 (EDT) From: Trevor Johnson <trevor@jpj.net> To: questions@FreeBSD.ORG Subject: Re: why FFS is THAT slower than EXT2 ? Message-ID: <Pine.BSI.3.95.991027210142.17462B-100000@blues.jpj.net> In-Reply-To: <199910272148.QAA10727@chiba.3jane.net>
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I'm not using soft updates, and I didn't have the "sync" option in
/etc/fstab because I, from the warning about the "async" flag in the
mount(8) man page, I assumed synchronous writes were the default:
$ cat /etc/fstab
# Device Mountpoint FStype Options Dump Pass#
/dev/wd0s1b none swap sw 0 0
/dev/wd0s1a / ufs rw 1 1
/dev/wd0s1f /usr ufs rw 2 2
/dev/wd0s1e /var ufs rw 2 2
/dev/wd2c /usr/ports ufs rw 2 2
proc /proc procfs rw 0 0
When I ran "mount" with no options, I was surprised to see it mention
asynchronous writes:
$ mount
/dev/wd0s1a on / (local, writes: sync 15 async 64)
/dev/wd0s1f on /usr (local, writes: sync 16 async 202)
/dev/wd0s1e on /var (local, writes: sync 132 async 197)
/dev/wd2c on /usr/ports (local, writes: sync 2 async 6)
procfs on /proc (local)
I added the "sync" option to /etc/fstab:
myname:/$ cat /etc/fstab
# Device Mountpoint FStype Options Dump
Pass#
/dev/wd0s1b none swap sw 0 0
/dev/wd0s1a / ufs rw,sync 1 1
/dev/wd0s1f /usr ufs rw,sync 2 2
/dev/wd0s1e /var ufs rw,sync 2 2
/dev/wd2c /usr/ports ufs rw,sync 2 2
proc /proc procfs rw 0 0
I rebooted with the new fstab, and now "mount" tells me my filesystems are
mounted synchronously, but still says there are asynchronous writes:
$ mount
/dev/wd0s1a on / (local, synchronous, writes: sync 617 async 317)
/dev/wd0s1f on /usr (local, synchronous, writes: sync 1338 async 435)
/dev/wd0s1e on /var (local, synchronous, writes: sync 770 async 215)
/dev/wd2c on /usr/ports (local, synchronous, writes: sync 3359 async 1088)
procfs on /proc (local)
The difference in the "mount" output seems to suggest that initially the
filesystems weren't mounted synchronously, and that even when they are,
some information is still written asynchronously. Is that the case? If
so, what is the default and how can I change it? I have a
3.3-19990924-STABLE kernel and 3.3-19990904 userland.
BTW, here are a couple of sections from the Linux mount(8) page:
defaults
Use default options: rw, suid, dev, exec,
auto, nouser, and async.
[...]
Some Linux file systems don't support -o sync (the ext2fs
does support synchronous updates (a la BSD) when mounted
with the sync option).
__
Trevor Johnson
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