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Re: [Xen-users] Network based storage - NBD/AoE/iSCSI other?

On Mon, 2 Oct 2006, John Madden wrote:
(Saturating the link is fine as long as your performance is good as
well.)  Anyway, the numbers I've read from them show something in the
neighborhood of really terrible:
http://www.linuxjournal.com/article/8149 -- 23.58MB/s reads.  I'd expect
that performance out of a single ATA disk. IOPS is obviously something
different, but I don't believe that article mentions it.

I find disk benchmarks with dd amusing. I soppose it works if all you are using it for is backup and other sequential tasks- but for my load, you'd want to benchmark 20 parallel dd processes, and then latency is more important than throuput.

The funny thing is, IDE does usually win the thruput race, if you stripe/raid over a couple busses- 23MB/sec is a lot less than I would expect in a sequential transfer from 10+ ide disks.

Still, we saw the same thing on our (horribly overpriced) EMC NAS at one of the the last places I worked- I think the partition we were testing had 4 10KRPM scsi drives, and it had 4GB of cache (in a redundant configuration, running in write-back mode) and it had something like 6 gigE connections. from one box, we got mediocre sequential speed; but we found that we could do the same transfer from 10 seperate client boxes, and still get the same speed from each client- making it not so mediocre after all.

(I would be quite suprised if the corraid box could stack up to the $100K+ EMC, even given the AoE advantage. (the EMC was NFS) but my point is that being able to adaquately service multiple clients is usually more important than sequential transfer to just one)

oh, also; Jumbo Frames make more difference than the NFS server used for large transfers over NFS; I do not know how true that is of AoE, but if I were troubleshooting slow AoE access, jumbo frames would be one of the first things I'd try.


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