>>> Kenneth Marshall <ktm(at)rice(dot)edu> wrote:
> On Thu, Sep 11, 2008 at 06:18:37PM +0100, Matthew Wakeling wrote:
>> On Thu, 11 Sep 2008, Laszlo Nagy wrote:
>>> So the basic system will reside on a RAID 1 array, created from two
SAS
>>> disks spinning at 15 000 rpm. I will buy 10 pieces of Seagate
Barracuda
>>> 320GB SATA (ES 7200) disks for the rest.
>>
>> That sounds good. Put RAID 1 on the pair, and RAID 1+0 on the rest.
It'll
>> be pretty good. Put the OS and the WAL on the pair, and the database
on the
>> large array.
>>
>> However, one of the biggest things that will improve your
performance
>> (especially in OLTP) is to use a proper RAID controller with a
>> battery-backed-up cache.
>
> But remember that putting the WAL on a separate drive(set) will only
> help if you do not have competing I/O, such as system logging or
paging,
> going to the same drives. This turns your fast sequential I/O into
> random I/O with the accompaning 10x or more performance decrease.
Unless you have a good RAID controller with battery-backed-up cache.
-Kevin