From: | Mark Kirkwood <markir(at)paradise(dot)net(dot)nz> |
---|---|
To: | Mikael Carneholm <Mikael(dot)Carneholm(at)WirelessCar(dot)com> |
Cc: | Alex Hayward <xelah-pgsql(at)xelah(dot)com>, Pgsql performance <pgsql-performance(at)postgresql(dot)org> |
Subject: | Re: Hardware: HP StorageWorks MSA 1500 |
Date: | 2006-04-24 23:57:34 |
Message-ID: | 444D65EE.6040605@paradise.net.nz |
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Lists: | pgsql-performance |
Mikael Carneholm wrote:
>
>> There are two SCSI U320 buses, with seven bays on each. I don't know
> what the overhead of SCSI is, but you're obviously not going to get >
> 490MB/s for each set of seven even if the FC could do it.
>
You should be able to get close to 300Mb/s on each SCSI bus - provided
the PCI bus on the motherboard is 64-bit and runs at 133Mhz or better
(64-bit and 66Mhz give you a 524Mb/s limit).
>
>> Of course your database may not spend all day doing sequential scans
> one at a time over 14 disks, so it doesn't necessarily matter...
>
Yeah, it depends on the intended workload, but at some point most
databases end up IO bound... so you really want to ensure the IO system
is as capable as possible IMHO.
>
> That's probably true, but *knowing* that the max seq scan speed is that
> high gives you some confidence (true or fake) that the hardware will be
> sufficient the next 2 years or so. So, if dual 2GBit FC:s still don't
> deliver more than 200Mb/s, what does?
>
Most modern PCI-X or PCIe RAID cards will do better than 200Mb/s (e.g.
3Ware 9550SX will do ~800Mb/s).
By way of comparison my old PIII with a Promise TX4000 plus 4 IDE drives
will do 215Mb/s...so being throttled to 200Mb/s on modern hardware seems
unwise to me.
Cheers
Mark
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