On Sun, 29 Jul 2001, Chris Bednar wrote:
> > there are some slight problems with xfs over software raid5 that have just
> > been fixed in the CVS tree. There were also IO stall problems with this
> > setup when you have a internal log. Basically you also want to make the log
> > an external log which has a large performance boost.
> > Search the archive for discussion about this. 1 week ago it was discussed
> > and it has some bencmarks to back it up.
> I've seen them. For some reason, I'm suspicious that this
> is a different problem.
> An external log is scary to me; I can afford lackluster
> write performance easier than I can afford:
> ``You know that $16k RAID setup you bought? it's gone to Hell
> because the one disk I was using for the log croaked.''
> ``You know that big RAID system? Well, I moved it from one
> machine to another, and now it won't work.''
Then make sure it's on a raid1 disk. And mark it with bright red labels.
Otherwise you have a $16k raid setup that won't perform.
Btw, if you do a clean umount and then move it you might have
lost the log but you won't have lost the files.
> In my opinion, an internal log has to work reasonably well for
> XFS to be viable. It's fine, of course, if an external log works
> better, and I don't mind doing that on my own systems.
It's called flexibility ;)
There must be a reason that it was originally thought off.
> I'll take a shot at CVS... by the way, is an internal log
> also a performance issue on IRIX systems?
The issue with a log on raid5 is only valid for software raid5. I have
seen no such issues with a hardware raid5 IIRC.
It's just that the md raid code got in the way of the log.