On 2003-07-16 19:57:22 -0700, Balazs Wellisch wrote:
> We're now stuck on the question of what type of RAID configuration to use
> for this server. RAID 5 offers the best fault tolerance but doesn't perform
> all that well. RAID 10 offers much better performance, but no hot swap. Or
> should we not use RAID at all. I know that ideally the log (WAL) files
> should reside on a separate disk from the rest of the DB. Should we use 4
> separate drives instead? One for the OS, one for data, one for WAL, one for
> swap? Or RAID 10 for everything plus 1 drive for WAL? Or RAID 5 for
> everything?

We have recently run our own test (simulating our own database load) on a new
server which contained 7 15K rpm disks. Since we always want to have a
hot-spare drive (servers are located in a hard-to-reach datacenter) and we
always want redundancy, we tested two different configurations:
- 6 disk RAID 10 array, holding everything
- 4 disk RAID 5 array holding postgresql data and 2 disk RAID 1 array holding
  OS, swap and WAL logs

Our database is used for a very busy community website, so our load contains a
lot of inserts/updates for a website, but much more selects than there are

Our findings were that the 6 disk RAID 10 set was significantly faster than
the other setup.

So I'd recommend a 4-disk RAID 10 array. I'd use the 5th drive for a hot-spare
drive, but that's your own call. However, it would be best if you tested some
different setups under your own database load to see what works best for you.

Vincent van Leeuwen
Media Design - http://www.mediadesign.nl/

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