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