Re: which ext3 fs type should I use for postgresql

From: Matthew Wakeling <matthew(at)flymine(dot)org>
To: "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: which ext3 fs type should I use for postgresql
Date: 2008-05-15 11:29:40
Message-ID: Pine.LNX.4.64.0805151217490.16756@aragorn.flymine.org
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On Thu, 15 May 2008, Philippe Amelant wrote:
> using mkfs.ext3 I can use "-T" to tune the filesytem
>
> mkfs.ext3 -T fs_type ...
>
> fs_type are in /etc/mke2fs.conf (on debian)

If you look at that file, you'd see that tuning really doesn't change that
much. In fact, the only thing it does change (if you avoid "small" and
"floppy") is the number of inodes available in the filesystem. Since
Postgres tends to produce few large files, you don't need that many
inodes, so the "largefile" option may be best. However, note that the
number of inodes is a hard limit of the filesystem - if you try to create
more files on the filesystem than there are available inodes, then you
will get an out of space error even if the filesystem has space left.
The only real benefit of having not many inodes is that you waste a little
less space, so many admins are pretty generous with this setting.

Probably of more use are some of the other settings:

-m reserved-blocks-percentage - this reserves a portion of the filesystem
that only root can write to. If root has no need for it, you can kill
this by setting it to zero. The default is for 5% of the disc to be
wasted.
-j turns the filesystem into ext3 instead of ext2 - many people say that
for Postgres you shouldn't do this, as ext2 is faster.

Matthew

--
The surest protection against temptation is cowardice.
-- Mark Twain

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