EMC – FAST Cache and LUN expansion or shrink operations

Someone on twitter asked me about a white paper they were reading on the EMC site recently that suggested that LUN expansion or shrink operations would require that FAST Cache be disabled. The white paper in question is located here. For those of you loitering on Powerlink the EMC Part Number is h8046.7. In any case, on page 8 it covers a number of requirements for using FAST Cache – most of which seem fairly reasonable. However, this one kind of got my attention (once my attention was drawn to it by @andrewhatfield) – “Once FAST Cache has been created, expansion or shrink operations require disabling the cache and re-creating the FAST Cache“. Wow. So if I want to do a LUN expansion I need to delete and re-create FAST Cache once it’s complete? Seriously? I informally confirmed this with my local Account TC as well.

It takes a while to create FAST Cache on a busy VNX. It takes even longer to disable it on a busy system. What a lot of piss-farting around to do something which used to be a fairly trivial operation (the expansion I mean). Now, I’ll be straight with you, I haven’t had the opportunity to test what happens if I don’t disable FAST Cache before I perform these operations. Knowing my luck the damn thing will catch on fire. But it’s worth checking this document out before you pull the trigger on FAST Cache.

[Edit: Or maybe they mean if you want to expand or shrink the FAST Cache? Because that makes sense. I hope that’s what they mean.]

[Edit #2: Joe (@virtualtacit) kindly clarified that this requirement relates to the shrinking or expansion of FAST Cache, not LUNs. My bad! Nothing to see here, move along :)]


  1. Go pull a vault drive and watch FAST cache go degraded. Although naviseccli still reports it as enabled for read / write, which would seem to indicate it is a furphy. That said, i haven’t been able to confirm the effects of the error via Analyzer.

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