Re: WAL+Os on a single disk

On Wed, 23 Jun 2010, Scott Marlowe wrote:
>> We have a 12 x 600G hot swappable disk system (raid 10)
>> and 2 internal disk  ( 2x 146G)
>>
>> Does it make sense to put the WAL and OS on the internal disks
>
> So for us, the WAL and OS and logging on the same data set works well.

Generally, it is recommended that you put the WAL onto a separate disc to
the data. However, in this case, I would be careful. It may be that the 12
disc array is more capable. Specifically, it is likely that the 12-disc
array has a battery backed cache, but the two internal drives (RAID 1
presumably) do not. If this is the case, then putting the WAL on the
internal drives will reduce performance, as you will only be able to
commit a transaction once per revolution of the internal discs. In
contrast, if the WAL is on a battery backed cache array, then you can
commit much more frequently.

Test it and see.

Matthew

--
 I don't want the truth. I want something I can tell parliament!
                                              -- Rt. Hon. Jim Hacker MP