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Re: Tables on multiple disk drives

From: Craig Thomas <craiger(at)osdl(dot)org>
To: <scott(dot)marlowe(at)ihs(dot)com>
Cc: <lists2(at)tokar(dot)ru>, <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Tables on multiple disk drives
Date: 2004-02-17 17:35:38
Message-ID: 64789.4.5.9.170.1077039338.squirrel@www.osdl.org (view raw or flat)
Thread:
Lists: pgsql-performance
> On Tue, 17 Feb 2004, Konstantin Tokar wrote:
>
>> Hi!
>> Does PostgreSQL allow to create tables and indices of a single
>> database on multiple disk drives with a purpose of increase
>> performance as Oracle database does? If a symbolic reference is the
>> only method then the next question is: how can it be determined what
>> file is referred to what table and index?
>
> You're life will be simpler, and your setup will be faster without
> having  to muck about with it, if you just buy a good RAID controller
> with battery  backed cache.  LSI/Megaraid and Adaptec both make
> serviceable controllers  for reasonable prices, and as you add drives,
> the speed just goes up, no  muddling around with sym links.

This works to a limited extent.  For very large databases, maximum
throughput of I/O is the paramount factor for database performance.  With
raid controllers, your LUN is still limited to a small number of disks.
PostgreSQL can only write on a file system, but Oracle, SAP DB, DB2, etc
can write directly to disk (raw I/O).  With large databases it is
advantageous to spread a table across 100's of disks, if the table is
quite large.  I don't know of any manufacturer that creates a 100 disk
raid array yet.

Some of the problem can be addressed by using a volume manager (such as
LVM in Linux, or Veritas on Unix-like systems).  This allows one to
create a volume using partitions from many disks.  One can then create
a file system and mount it on the volume.

However, to get the best performance, Raw I/O capability is the best
way to go.
>
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