Followup to slow SAN speed

I mentioned this morning that I was having slow SAN performance. I said that I’d post an update if I figured out what was wrong, and I did.

EMC AX4-5’s with a single processor have a known issue, apparently. Since there’s only one storage controller on the unit, it intentionally disables write cache. Oops. I didn’t even have to troubleshoot with the engineer. It was pretty much “Do you only have one processor in this?” “yes” “Oh, well, there’s your problem right there”.

So yea, if you’re thinking about an EMC AX4-5, make sure to pony up the extra cash…err..cache..err..whatever.

  • JeffHengesbach

    This is one of those things sales/account managers/engineers need to mention during pre-sales discussions…..

  • Matt


    Exactly. The “we’ll sell this to you, but we hope you aren’t actually going to USE it for anything” speech would have been nice.

  • chewyfruitloop

    we have an ax-150 in the rack
    if it looses power to one of the psu’s, the associated controller goes down too and the write cache dies

    i think it must be a product family thing

    once you get the power back, you still have to make sure its brought the cache back though

  • Matt


    Just for the sake of knowing, what do you have to do to make sure the cache starts (and how do you correct it?)

  • Anonymous

    Glad to know. I won’t be purchasing any EMC products in the near future

  • chewyfruitloop

    the only real thing you can do from the admin console (aka web interface) is check the storage processor a and b are up

    the only time i’ve had to intervene is when i had a full shutdown of the server room
    i think the problem there was the server thats attached to it by fiber was down, but once i’d given it the reboot nudge it needed then it all came back to life

    i think these things are cheep (compared to normal emc kit) because they run windows xp embedded

    during bubble 1.0 in 2000 we had a symetrix box in the server room with a full terabyte of disk in a mirrored array, that thing was so expensive the admin console was a laptop emc had bolted to the indside of the front door (this thing was the same size a 42u rack and about half as wide again)

    having trawled through the ax series docs a while back though, it did say that both processors needed to be up for write caching
    you would think they’d have figured out a way to make it work on only one cpu though. the 150 came with its own 1u ups to power one cpu all the time to ensure the cache was fully written to the disks if it lost power to the other

    sorry a bit rambely this