On 03/12/2013 05:49 PM, Gregg Jaskiewicz wrote:
So out of 6 disks then having 4 in Raid 1+0 configuration and other two in mirror for WAL. That's another option then for me to test.
That is an option, but it's not necessarily a good one. If all you have are six disks, you are probably better off just doing a big RAID-10 for everything.
As Alban mentioned, you would do best to stay away from RAID-5 as that will basically obliterate your write speeds, which is especially critical for WAL files.
There is one caveat to all of this, of course. What you plan to use the server for has a critical impact on these decisions.
What it boils down to, is that six spindles is not very many. You don't really have enough to dedicate any to your WAL files without drastically cutting the available IOPS for your regular data. In addition, with any of these setups, you'll want a hot spare in case of drive failure. If you have six disks available, you really only have five. That's not an even number, so one is wasted in RAID-10, and you may find in your RAID-5 tests that it doesn't work well for long-term use.
The truth is that you can get by for quite a while on this no matter how you split up those six spindles. Until you need a lot of heavy disk reads or writes. Then it's going to hurt. So ask yourself what kind of load or usage you expect, and plan accordingly.
I have to tell you though, we had a server with twelve spindles three years ago, and it barely kept up with our transaction load. We had two hot spares, a RAID-1, and 8-disks in a RAID-10. Several pgbench tests back then showed that our RAID-10 could only adequately serve 1800TPS directly, and we needed at least 6000. Ultimately, it lead to us switching to NVRAM (SSD) for high TPS data, and creating a tablespace on a RAID-10 for archived or low-priority data.
But we got by on those original 12 spindles for a couple years. If your data needs are less, you can probably do OK with six. For a while, anyway. :)
-- Shaun Thomas OptionsHouse | 141 W. Jackson Blvd. | Suite 500 | Chicago IL, 60604 312-676-8870 sthomas@xxxxxxxxxxxxxxxx ______________________________________________ See http://www.peak6.com/email_disclaimer/ for terms and conditions related to this email -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
