Re: Redundant file server for postgres

Robert Powell wrote:
> To whom it may concern,
>
>
>
> I'm looking for a file server that will give me a high level of
> redundancy and high performance for a postgres database.
For strong redundancy and availability you may need a secondary server
and some sort of replication setup (be it a WAL-following warm spare,
slony-I, or whatever). It depends on what you mean by "high".

As for performance - I'm still learning on this myself, so treat the
following as being of questionable accuracy.

As far as I know the general rule for databases is "if in doubt, add
more fast disks". A fast CPU (or depending on type of workload several
almost-as-fast CPUs) will be nice, but if your database is big enough
not to fit mostly in RAM you'll mostly be limited by disk I/O. To
increase disk I/O performance, in general you want more disks. Faster
disks will help, but probably not as much as just having more of them.

More RAM is of course also nice, but might make a huge difference for
some workloads and database types and relatively little for others. If
doubling your RAM lets the server cache most of the database in RAM
it'll probably speed things up a lot. If doubling the RAM is the
difference between 2% and 4% of the DB in RAM ... it might not make such
a difference (unless, of course, your queries mostly operate on a subset
of your data that's fairly similar to your RAM size, you do lots of big
joins, etc).

Various RAID types also have implications for disk I/O. For example,
RAID-5 tends to have miserable write performance.

In the end, though, it depends a huge amount on your workload. Will you
have huge numbers of simpler concurrent transactions, or relatively few
heavy and complex ones? Will the database be read-mostly, or will it be
written to very heavily? Vaguely how large is your expected dataset? Is
all the data likely to be accessed with equal frequency or are most
queries likely to concentrate on a small subset of the data? And so on...

--
Craig Ringer