On Thu, Dec 06, 2012 at 01:18:38PM -0300, Roberto Scattini wrote:
> hi, i have a new dell r720 server with 5 600gb disks.
> his function will be a postgresql server (the size of the databases is
> really small with 600gb we should be fine for a long time).
>
> which raid configuration would you recommend?
> i was thinking in raid 5 with all five disks but i am not a expert.
>
> i prefer redundandcy against size (i mean, i can sacrifice space). and i
> dont want performance degradation for doing raid with an incorrect number
> of disks.
I'll be the first one in this thread to recommend ZFS [1]. With 5 disks, I
would personally do a RAID-1+0, with a hot spare. A RAID-1 will outperform
a parity-based RAID using the same disks every time, due to calculating the
parity. Further, striping across two mirrors will give increased
performance that parity-based RAID cannot achieve. Lastly, you can suffer
any sort of disk failures, provided all mirrors in the stripe remains in
tact.
1: http://zfsonlinux.org
If you must absolutely do a parity-based RAID, then I would suggest a
5-disk RAIDZ-1 without a hot spare. It's "best practice" to use the power
of two, plus parity for your number of disks. In this case, it will give
you the best performance, decent space, and allow for 1 disk failure.
Further, I would recommend the investment in two Intel 300-series SSDs. You
can then partition the SSDs giving 1 GB on each in a mirrored ZIL, and the
rest to a striped L2ARC. For a PostgreSQL DB, you will see immensive
performance gains that you cannot achieve with Linux-based software RAID
and filesystems. And, because ZFS is also a volume manager, there is no
need for LVM and the cache troubles it's plagued with [2].
2: http://serverfault.com/questions/279571/lvm-dangers-and-caveats
If interested, I've been blogging on this very topic. You can see the
relevent posts to your setup here:
* Installing ZFS on Debian: http://pthree.org/?p=2357
* The ZIL: http://pthree.org/?p=2592
* The ZFS ARC: http://pthree.org/?p=2659
Just my $.02.
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