Date: Thu, 27 Dec 2007 11:18:52 -0500
From: Jean-David Beyer <jeandavid8@verizon.net>
Subject: Re: With 4 disks should I go for RAID 5 or RAID 10
In-reply-to: <47735156.2080403@Sheeky.Biz>
To: 'pgsql-performance' <pgsql-performance@postgresql.org>
Message-id: <4773D06C.2020205@verizon.net>
Organization: Institute for Regimented Whimsey
MIME-version: 1.0
Content-type: text/plain; charset=ISO-8859-1
Content-transfer-encoding: 7bit
References: <0f9701c84801$399dcff0$8f01010a@iptel.com.ar>
	<47731D32.3040403@Sheeky.Biz> <47732BCB.2090302@mark.mielke.cc>
	<47735156.2080403@Sheeky.Biz>
User-Agent: Thunderbird 1.5.0.9 (X11/20070317)

Shane Ambler wrote:

>> I achieve something closer to +20% - +60% over the theoretical 
>> performance of a single disk with my four disk RAID 1+0 partitions.
> 
> If a good 4 disk SATA RAID 1+0 can achieve 60% more throughput than a 
> single SATA disk, what sort of percentage can be achieved from a good 
> SCSI controller with 4 disks in RAID 1+0?
> 
> Are we still hitting the bus limits at this point or can a SCSI RAID 
> still outperform in raw data throughput?
> 
> I would still think that SCSI would still provide the better reliability 
> that it always has, but performance wise is it still in front of SATA?
> 
I have a SuperMicro X5DP8-G2 motherboard with two hyperthreaded
microprocessors on it. This motherboard has 5 PCI-X busses (not merely 5
sockets: in fact it has 6 sockets, but also a dual Ultra/320 SCSI controller
chip, a dual gigabit ethernet chip.

So I hook up my 4 10,000 rpm database hard drives on one SCSI controller and
the two other 10,000 rpm hard drives on the other. Nothing else is on the
SCSI controller or its PCI-X bus that goes to the main memory except the
other SCSI controller. These PCI-X busses are 133 MHz, and the memory as 266
MHz but the FSB runs at 533MHz as the memory modules are run in parallel;
i.e., there are 8 modules and they run two at a time.

Nothing else is on the other SCSI controller. Of the two hard drives on the
second controller, one has the WAL on it, but when my database is running
something (it is up all the time, but frequently idle) nothing else uses
that drive much.

So in theory, I should be able to get about 320 megabytes/second through
each SCSI controller, though I have never seen that. I do get over 60
megabytes/second for brief (several second) periods though. I do not run RAID.

I think it is probably very difficult to generalize how things go without a
good knowledge of how the motherboard is organized, the amounts and types of
caching that take place (both sortware and hardware), the speeds of the
various devices and their controllers, the bandwidths of the various
communication paths, and so on.


-- 
  .~.  Jean-David Beyer          Registered Linux User 85642.
  /V\  PGP-Key: 9A2FC99A         Registered Machine   241939.
 /( )\ Shrewsbury, New Jersey    http://counter.li.org
 ^^-^^ 11:00:01 up 10 days, 11:30, 2 users, load average: 4.20, 4.20, 4.25