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Re: Hardware: HP StorageWorks MSA 1500

From: "Mikael Carneholm" <Mikael(dot)Carneholm(at)WirelessCar(dot)com>
To: "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 20:38:12
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Lists: pgsql-performance
> If I'm reading the original post correctly, the biggest issue is 
> likely to be that the 14 disks on each 2Gbit fibre channel will be 
> throttled to 200Mb/s by the channel , when in fact you could expect 
> (in RAID 10
> arrangement) to get about 7 * 70 Mb/s = 490 Mb/s.

> The two controllers and two FC switches/hubs are intended for
redundancy, rather than performance, so there's only one 2Gbit channel.
I > don't know if its possible to use both in parallel to get better

> I believe it's possible to join two or more FC ports on the switch
together, but as there's only port going to the controller internally
this presumably wouldn't help.

> 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.

Darn. I was really looking forward to ~500Mb/s :(

> 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...

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?



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