Hi, hope you don't mind if I make some portions of your email public in
a reply--I hadn't seen it come through on the list at all, so it's no
duplicate to me.
Johansen wrote:
> Adam:
>
> Sorry if this is a duplicate, I had issues sending e-mail this morning.
>
> Based upon your CPU choices, I think you shouldn't have a problem
> saturating a GigE link with a pair of Operton 275's. Just as a point of
> comparison, Sun sells a server with 48 SATA disks and 4 GigE ports:
>
> http://www.sun.com/servers/x64/x4500/specs.xml
>
> You have fewer disks, and nearly as much CPU power as the x4500. I
> think you have plenty of CPU in your system.
>
> Your RAID controllers have as many SATA ports as the SATA cards in the
> x4500, and you seem to have the same ratio of disks to controllers.
I'm well aware of the Thumper, and it's fair to say it was an
inspiration, just without two-thirds of the capacity or any of the
serious redundancy. I also used the X4500 as a guide for
> I suspect that if you have a bottleneck in your system, it would be due
> to the available bandwidth on the PCI bus.
Mm. yeah, it's what I was worried about, too (mostly through ignorance
of the issues), which is why I was hoping HyperTransport and PCIe were
going to give that data enough room on the bus.
But after others expressed the opinion that the Areca PCIe cards were
overkill, I'm now looking to putting some PCI-X cards on a different
(probably slower) motherboard.
> Caching isn't going to be a huge help for writes, unless there's another
> thread reading simultaneoulsy from the same file.
>
> Prefetch will definitely use the additional RAM to try to boost the
> performance of sequential reads. However, in the interest of full
> disclosure, there is a pathology that we've seen where the number of
> sequential readers exceeds the available space in the cache. In this
> situation, sometimes the competeing prefetches for the different streams
> will cause more temporally favorable data to be evicted from the cache
> and performance will drop. The workaround right now is just to disable
> prefetch. We're looking into more comprehensive solutions.
Interesting. So noted. I will expect to have to test thoroughly.
>> I understand I'm not going to get terribly far in thought experiment
>> mode, but I want to be able to spec a box that balances cheap with
>> utility over time.
>
> If that's the case, I'm sure you could get by just fine with the pair of
> 275's.
Thanks,
adam
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