> Another important change is that it is no longer necessary to run
> tunefs in single user mode to activate soft updates. All that is
> needed is to add the "softdep" mount option to the partitions you
> want soft updates enabled on in /etc/fstab."
[.....]
> I especially like not having to run tunefs :-)
[.....]
Having the softdep option in fstab(5) doesn't gel well with the
recent background-fsck work being introduced by Kirk - although it
works from what I can tell.
In both OpenBSD and NetBSD, a filesystem mounted with the ``softdep''
option will update the super-block flags with the FS_DOSOFTDEP bit, so
it's easy for fsck(8) to tell how an unclean filesystem was last
mounted. In fact, OpenBSD has ``if 0''d code that allows unclean
filesystem mounts if they have that FS_DOSOFTDEP bit set (NetBSD
doesn't seem to have this).
The problem I think is where a ``mount -u'' is done to downgrade a
filesystem from soft-udpates to no soft-updates. Both OpenBSD and
NetBSD have comments to the effect
/*
* Flush soft dependencies if disabling it via an update
* mount. This may leave some items to be processed,
* so don't do this yet XXX.
*/
and both ignore the problem (leaving soft-updates set). I don't
think there's a satisfactory way of doing this - in much the same way
as downgrading a read-write filesystem to read-only doesn't quite
work. If certain operations are in effect (like a background fsck in
the first instance or a reference is held to a file with a zero link
count in the second), all hell can break loose.
Having said all that, I quite like the softdep option in OpenBSD &
NetBSD, despite it only being a half-option :-)
> The second improvement, contributed by
> [EMAIL PROTECTED], is a new directory allocation policy (codenamed
> "dirpref"). Coupled with soft updates, the new dirpref code offers up
> to a 60x speed increase in gluk's tests, documented here:"
>
>
>http://groups.google.com/groups?q=dirpref&num=100&hl=en&lr=&safe=off&rnum=2&seld=905073910&ic=1
>
I do like the dirpref stuff, but I can't comment much on it
except that it looks like a good change that should be fairly easy to
bring into FreeBSD.
I'm not 100% convinced about the algorithm to avoid clusters filling
up with directory-only entries (it looks like a worst-case would fill
a cluster with 50% directories and 50% files leaving a bad layout when
the directories are populated further), but then the non-dirpref
scheme has some far worse worst-case scenarios ;-)
--
Brian <[EMAIL PROTECTED]> <brian@[uk.]FreeBSD.org>
<http://www.Awfulhak.org> <brian@[uk.]OpenBSD.org>
Don't _EVER_ lose your sense of humour !
To Unsubscribe: send mail to [EMAIL PROTECTED]
with "unsubscribe freebsd-current" in the body of the message
