| From: | Greg Smith <gsmith(at)gregsmith(dot)com> |
|---|---|
| To: | pgsql-performance <pgsql-performance(at)postgresql(dot)org> |
| Subject: | Re: 12 disks raid setup |
| Date: | 2008-03-01 04:56:54 |
| Message-ID: | Pine.GSO.4.64.0802292347250.145@westnet.com |
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| Lists: | pgsql-performance |
On Sat, 1 Mar 2008, Shane Ambler wrote:
> It may be the way you have worded this but it makes it sound like the
> cache and the battery backup are as one (or that the cache doesn't work
> unless you have the battery)...If the raid card has the cache without
> the battery you would get the performance figures you mentioned, you
> just wouldn't have the reliability of finishing writes after a power off
> situation.
Wording is intentional--if you don't have a battery for it, the cache has
to be turned off (or set to write-through so it's only being used on
reads) in order for the database to be reliable. If you can't finish
writes after a power off, you can't cache writes and expect your database
to survive for too long.
--
* Greg Smith gsmith(at)gregsmith(dot)com http://www.gregsmith.com Baltimore, MD
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