SAN performance issues with the new install

Date May 27, 2009

So, you would think that 12 spindles would be...you know...fast.

Even if you took 12 spindles, made them into a RAID 10 array, they'd still be fast.

That's what I'd think, anyway. It turns out, my new EMC AX4 is having a bit of a problem. None of the machines hooked to it can reach > 30MB/s (which is 240Mb/s in bandwidth-talk). I haven't been able to determine the bottleneck yet, either.

I've discounted the switch. The equipment is nearly identical to that in the existing primary site (using SATA in the backup rather than SAS, but still, 30MB?). It isn't the cables. Port speeds read correctly (4GB from the storage array, 2GB from the servers).

The main difference is that the storage unit only has one processor, but I can't bring myself to believe that one processor can't push/pull over 30MB/s. I originally had it arranged as RAID 6, and I thought that maybe the two checksum computations were too much for it, but now with RAID 10, I'm seeing the same speed, so I don't think the processor is the bottleneck.

I'm just plain confused. This morning I'm going to be calling EMC. I've got a case open with their tech support, so hopefully I'll be able to get to the bottom of it. If it's something general, I'll make sure to write about it. If it's the lack of a 2nd storage processor, I'll make sure to complain about it. Either way, fun.

3 Responses to “SAN performance issues with the new install”

  1. jronnblom said:

    If you only have one SP in the AX4 then I believe that the AX4 won't enable the write cache. And you might also need the UPS module but they call it a SPS.

    -J

  2. Daybrinjer said:

    Your bottleneck should be your networking gear, such as your gigabit switch. Since you are not able to get above that here are some of the more obscure issues that I have ran into... Failure to initialize disks in the correct way and Vista doesn't like to use a lot of bandwidth while streaming music.

  3. Matt said:

    @Daybrinjer

    /me scratches head

    I think one of us is misunderstanding the other, but I'm honestly not sure which.

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