EMC – FAST and FAST Cache on the CX4-960

Apologies for the lack of posts over the last few months – I have been nuts deep in work and holidays. I’m working on some literature around Storage Pools and FAST in general, but in the meantime I thought I’d share this nugget with you. We finally got approval to install the FAST and FAST Cache enablers on our production CX4-960s a few nights ago. We couldn’t install them on one of the arrays because we had a dead disk that prevented the NDU from going ahead. Fair enough. Two awesome things happened when we installed it on the other array. Both of which could have been avoided if I’d had my shit together. Firstly, when I got into the office the next morning at 8 am, we noticed that the Read Cache on the array was disabled. For those of you playing at home, we had the cache on the 960 set at 1000MB read and 9760MB for write. I think I read this in a whitepaper some where. But after FAST went on, we still had 9760MB allocated to Write, and 0MB available for Read. Awesome not so much. Seems that we lost 1000MB, presumably because we added another layered application. Funnily enough we didn’t observe this behaviour on our lab CX4-120s, although you could argue that they really have sweet FA of cache in the first place. So now we have 8760MB for Write, and 1000MB for Read. And I’m about to configure a few hundred GB of FAST Cache on the EFDs in any case. We’ll see how that goes.

The other slightly boneheaded thing we did was forget to trespass the LUN ownership of LUNs on SP A back from SP B. In other words, an NDU applies code to SP B first, reboots the SP, checks it, and then loads code on the other SP. As part of this, LUN ownership is temporarily trespassed to the surviving SP (this is the whole non-disruptive thing). Once the NDU is complete, you should go and check for trespassed LUNs and move them back to their owners. Or not, and have everything run on one SP for a while. And wait for about 9000 Exchange users to complain when one of the Exchange clusters goes off-line. Happy days.