[Techtalk] Journalling file systems.

[Malcolm Tredinnick]

I'm not going to give any comparisons, since I pretty much chose one and
went with it. But I can possibly clear up some issues with ext3.

On Sat, Oct 27, 2001 at 09:45:46AM +1000, Mary Gardiner wrote:
> Well, journalling file systems seem to be all the rage at the moment :)
> and I have to say that I would be grateful not to have to sit through an
> fsck every time a circuit breaker triggers.
> 
> At the moment, I'm using ext2fs and vfat (I'm not intending to drop the
> vfat, my Windows partition would be unhappy... :) )
> 
> I've been exposed to a three way holy war between xfs users, reiserfs
> users and ext3fs users, but not a very informative one.

That would possibly be because there is no right answer.

> I'm looking for a good rundown on their comparitive strengths.

Have a browse through the archives of the kernel-traffic summaries
(http://kt.zork.net/kernel-traffic/back-issues.html). Journalling
filesystem threads are often covered there and sometimes different
benchmarks are posted (which usually prove you can't prove anything).
A few are mentioned, for example, in the thread at
http://kt.zork.net/kernel-traffic/kt20010910_132.html#1.

> I need:
>  * Something that works with the 2.4.x kernel series, I don't mind
>    applying patches (otherwise the options narrow considerably).
>  * Something stable, I'm going to run it on my personal box, and would
>    be most upset to lose a partition.
>
> I also use Maildirs, so something with good performance on a large
> number of small files would be good, although df tells me that I'll run
> out of room on /home long before running out of inodes.
> 
> I'm being sold the following strengths of each file system:
> 
> * Reiser: the aforementioned performance optimisation for large numbers
>   of small files, is part of the 2.4.x kernels and so doesn't require a
>   patch.
> * ext3: Can convert existing ext2 partitions without moving all the
>   data, formatting, and moving back. Can put the journal file on a
>   different partition so that the partition can be read as ext2 by, for
>   example, a boot floppy.

Having the journal on a different partition if, I believe, not
necessary. You can just mount the ext3 partition as type ext2 and it
will be fine. When converting all my systems over to ext3, I ran tune2fs
on different partitions, remounted a few as ext3, played around a bit,
then rebooted. They came back as ext2 and nothing appeared to have been
corrupted. This gave me some confidence that I wasn't about to destroy
my system.

> * xfs: None so far, although my housemates think it is 'cool'.

Hardly a winning argument.

> Weaknesses:
> * Reiser: Makes for an enormous kernel.[1]
> * ext3: Appears somewhat unstable, has caused hard locks for users.

Possibly hardware related. Have a look at
http://kt.zork.net/kernel-traffic/kt20011015_137.html#1, for example.

> * xfs: Again, none.
> 
> As you can see, technical details are scarce. Can anyone give me any
> pointers to a good rundown on any or all of these file systems (points
> to linux-kernel threads etc most appreciated), or share their
> experiences with any of these file systems especially as regards data
> integrity, system lockups, and failure? And, wrt ext3, is it a good idea
> to run the Linus kernel with patches, or the Alan Cox kernels?

I've been running the -ac kernels for a long time now. I found ext3
_very_ easy to get up and running and have experienced no problems with
it to date.

The evidence that finally convinced me to go with ext3 was a
conversation I had with Daniel Veillard at OLS this year. He runs the
rpmfind boxes (four of them) and has been using ext3 on both 2.2 and 2.4
kernels for over a year now. He has not lost a single byte due to
filesystem problems (a couple of hard drives crashed, but you can't
avoid that) and rpmfind get s a *LOT* of traffic. Also, some of those
machines are in slightly flakey environments and they had their fair
share of spontaneous reboots, so the journalling part was tested.

At the end of the day, all three are still being developed on Linux.
ResierFS has had its problems in the past, but all seem pretty good now
(I know people running each).

I think the correct solution is to line up three of your housemates, put
labels on their heads (Reiser, ext3 and xfs) and then swing about wildly
until you hit one. Choose that filesystem. Of course, I'd prefer if you
didn't credit me with this method of choosing when you are explaining it
to them. :)

Cheers,
Malcolm

-- 
"Very funny, Scotty. Now beam down my clothes."