Обсуждение: Question regarding the file system

Hi guys,

    I have been given a dual PIII with 768MB RAM and I am going to install
PostgreSQL on it, for data warehousing reasons. I have also been given four
160 Ultra SCSI disks (36MB each) with a RAID controller (Adaptec 2100). I
am going to use a RAID5 architecture (this gives me approximately 103 GB of
data) and install a Debian Linux on it: this machine will be dedicated
exclusively to PostgreSQL.

    I was wondering which file system you suggest me: ext3 or reiserfs?
Also, I was thinking of using the 2.6.x kernel which offers a faster thread
support: will PostgreSQL gain anything from it or should I stick with 2.4.x?

Thank you very much,
-Gabriele
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Current Location: Prato, Toscana, Italia
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Gabriele,

>     I have been given a dual PIII with 768MB RAM and I am going to install
> PostgreSQL on it, for data warehousing reasons. I have also been given four
> 160 Ultra SCSI disks (36MB each) with a RAID controller (Adaptec 2100). I
> am going to use a RAID5 architecture (this gives me approximately 103 GB of
> data) and install a Debian Linux on it: this machine will be dedicated
> exclusively to PostgreSQL.

FWIW, RAID5 with < 5 disks is probably the worst-performing disk setup for PG
with most kinds of DB applications.   However, with 4 disks you don't have a
lot of other geometries available.    If the database will fit on one disk, I
might suggest doing RAID 1 for 2 of the disks, and having two single disks,
one with the OS and swap, and one with the database log.

If you're doing Debian, make sure to get a current version of PG from Debian
Unstable.

>     I was wondering which file system you suggest me: ext3 or reiserfs?

These seem to be equivalent in data=writeback mode for most database
applications.   Use whichever you find easier to install & maintain.

> Also, I was thinking of using the 2.6.x kernel which offers a faster thread
> support: will PostgreSQL gain anything from it or should I stick with
> 2.4.x?

PostgreSQL won't gain anything from the thread support (unless you're using a
threaded front-end app with thread-safe ecpg).   But it will gain from
several other improvements in 2.6, especially better scheduling and VM
support.  Use 2.6.

--
Josh Berkus
Aglio Database Solutions
San Francisco

Gabriele,

> By any chance, do you have some reference or some tests that talk about the
> fact that RAID5 with less than 5 disks is not performing?

Just this list.  But it's easy to test yourself; run bonnie++ and compare the
performance of seeks and random writes (which PG does a lot of) vs. a plain
single disk.

--
--Josh

Josh Berkus
Aglio Database Solutions
San Francisco