On Thu, 15 May 2008, david@lang.hm wrote:
> On Thu, 15 May 2008, Matthew Wakeling wrote:
>
>> 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.
>
> IIRC postgres likes to do 1M/file, which isn't very largeas far as the -T
> setting goes.
>
>> 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.
>
> think twice about this. ext2/3 get slow when they fill up (they have
> fragmentation problems when free space gets too small), this 5% that only
> root can use also serves as a buffer against that as well.
>
>> -j turns the filesystem into ext3 instead of ext2 - many people say that
>> for Postgres you shouldn't do this, as ext2 is faster.
>
> for the partition with the WAL on it you may as well do ext2 (the WAL is
> written synchronously and sequentially so the journal doesn't help you), but
> for the data partition you may benifit from the journal.
a fairly recent article on the subject
http://www.commandprompt.com/blogs/joshua_drake/2008/04/is_that_performance_i_smell_ext2_vs_ext3_on_50_spindles_testing_for_postgresql/
David Lang
