Re: Filesystem options for storing pg_data

On 4/21/05, Marco Colombo <pgsql(at)esiway(dot)net> wrote:
> > > > Generally XFS and JFS are considered superior to ext2/3.
> > > Do you mind posting a reference? I'm really interested in the comparison
> > > but everytime I asked for a pointer, I got no valid resource, so far.
> Well, my point being the ones I find lead to the conclusion that EXT3 is
> "considered superior" to XFS and JFS. One for all:

First of all, my workload is not IO bound, so don't consider what
I write as solutions for IO heavy setups.

Personally I use ext3 (with ~128 KB per inode ratio, to save some
space and keep inodes more closely together), with noatime option.

I've tried JFS some time ago and got away from it soon after. The
reasons were that:
1. JFS dynamic inode allocation left less free space for apps than
ext3 (I usually decrease inode ratio to some reasonable limit
(like 4 times current ratio for given directory set)). (Yeah, not
a serious issue, yet I admit I tend to consider it).
2. FSCK. Back then JFS had an ugly feature of mounting only
'clean' filesystems, i.e. fsck had to be done in userspace
(unlike ext3 which does it as a part of mount process).
I don't know if it is still that way.
3. Performance. For my workload, mostly single threaded and
bursty, ext3 appeared a bit faster.

Yet it was a good while ago, JFS might have changed a good bit
since then. I have no experience with XFS, but I've heard a lot
of good about it.

> Again ext3 is the winner (among journalled fs), but by a small edge
> only. And again, there are a lot of variables. Using for example
> data=journal with a big journal file on a different disk would
> be extremely interesting, just as using a different disk for WALs
> is at PostgreSQL level (the result might be the same).

Some time ago I thought it could be nice thought experiment
to 'tune' ext3 for PostgreSQL needs. (Mark WAL files for
immediate updates, journal other updates (filesize changes,
creations etc), and keep journal close to WAL files... ;)

> I'm not stating that EXT3 is better. My opinion on the matter is that
> you shouldn't care about the filesystem much (EXT3, JFS, XFS being the
> same for _most_ purposes with PostgreSQL). That is, it's a small little
> spot in the big picture of performance tuning. You'd better look at the
> big picture.
>
> I'm only countering your claim:
> "Generally XFS and JFS are considered superior to ext2/3".

You can certainly say that XFS/JFS are more complex and were
engineered to better handle high work load. Ext3 is relatively
simple; and its simplicity may also be a big advantage when
handling high load.

Summary: I'm not arguing JFS/XFS are worser/same. All I want to say
is that ext3 is a decent filesystem. Ext3's greatest advantage, I guess,
is the ease of deployment -- it comes "out of the box" with most
distributions. With a little tuning it can perform reasonably well for
most needs.

Regards,
Dawid