Re: SAN vs Internal Disks - Mailing list pgsql-performance

From Florian Weimer
Subject Re: SAN vs Internal Disks
Date
Msg-id 82myvynb7p.fsf@mid.bfk.de
Whole thread Raw
In response to Re: SAN vs Internal Disks  (Arjen van der Meijden <acmmailing@tweakers.net>)
List pgsql-performance
* Arjen van der Meijden:

> The disadvantage of using Areca or 3Ware is obviously the lack of
> support in A-brand servers and the lack of support for SAS-disks. Only
> recently Areca has stepped in the SAS-market, but I have no idea how
> easily those controllers are integrated in standard servers (they tend
> to be quite large, which will not fit in 2U and maybe not even in 3U
> or 4U-servers).

Recent 3ware controllers are a bit on the hot side, too.  We had to
switch from two 12 port controllers to a single 24 port controller
because of that (combined with an unlucky board layout: the two 8x
PCIe connectors are next to each other).

Unfortunately, read performance maxes out at about 8 disks in a
RAID-10 configuration.  Software RAID-0 across hardware RAID-1 is
significantly faster (factor of 3 to 5 in low-level benchmarks).
However, it seems that something in this stack does not enforce write
barriers properly, so I don't think we will use this in production.

RAID-6 doesn't perform well, either (especially for several processes
reading different files sequentially).

We'll probably split the 24 disks into a couple of RAID-10s, and
distribute tables and indexes manually among the file systems.  This
is a bit disappointing, especially because the system is able to read
at 800+ MB/s, as shown by the software-RAID-on-hardware-RAID
configuration.

I haven't seen 24-disk benchmarks with Areca controllers.  A
comparison might be interesting.

--
Florian Weimer                <fweimer@bfk.de>
BFK edv-consulting GmbH       http://www.bfk.de/
Kriegsstraße 100              tel: +49-721-96201-1
D-76133 Karlsruhe             fax: +49-721-96201-99

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