On Tue, 2002-03-05 at 10:08, Stuart Levy wrote:
> Simon Matter suggested, re improving setup of a RAID-5:
> [...]
> > 2) The really important thing is how you set up the raid5 array. Did you
> > make an external log? That makes the BIG difference. I suggest this
> > layout:
> >
> > Every disk has:
> > Part1: 200M Part2: 8.8G
> > create raid1 on disk 1-2 / part 1
> > create swap on disk 3-8 / part1
> > create raid5 on disk 1-8 / part 2
> >
> > create XFS FS on raid5 with external log on raid1
>
> Just wondering about the importance of a redundant
> external log. I have a RAID-5 setup for the main filesystem
> data, but keep the log on a nonredundant partition of
> another drive, on the theory that if the log were lost,
> I shouldn't lose more than the last few seconds' activity.
>
> And it appears that xfs_repair -l /dev/newpartition -L /dev/maindevice
> can be used to initialize a new external log -- I won't need
> to re-create the entire filesystem or anything.
No, this will not do anything to the filesystem - might be an
interesting way to switch the log to external though. I think
the argument parsing needs some work here - I suspect you can
specify an external log on the mount line when you do not have
one in the filesystem.....
There is no way of moving the log without dump/mkfs/restore.
Steve
p.s. there is code coming which may fix the raid5 internal log
performance problem, but we have not had time to port it to linux
yet.
>
> (I tested the above create-new-log scenario, though only on a
> cleanly-unmounted filesystem.)
>
> Also, for performance, I imagine that it'd help a lot to have
> an external log on a *different spindle* than the
> main filesystem, to avoid lots of extra seeks.
> Since N disks fit in my system, I used N-1 for the RAID-5
> main xfs filesystem and the other 1 for the external log
> (and system disk). But if the ext log needed to be *both*
> redundant and to share no spindles with the main fs,
> I'd be limited to N-2 disks for XFS data, a big loss.
>
> Does this sound right?
>
> Stuart Levy, slevy@xxxxxxxxxxxxx
--
Steve Lord voice: +1-651-683-3511
Principal Engineer, Filesystem Software email: lord@xxxxxxx
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