EMC is set to release a new version of the FLARE operating system for CLARiiON CX4 arrays in the next couple weeks. This version, FLARE 30, includes a number of highly anticipated features and I have a lot of customers anxiously awaiting its availability. Two major new features are FAST (Fully Automated Storage Tiering) and FAST Cache, which Matt compares and contrasts here.
If you are interested in EMC’s new FAST (Fully Automated Storage Tiering) there are a few things to keep in mind. What I’m referring to is the new “Version 2″ of FAST which allows for sub-LUN automatic tiering of your data.
For a while now on EMC arrays we have carved and provisioned storage manually. That means we take a set of disks, usually 5 or 9 of them, and combine them in to a RAID Group to work together. We then “slice” up that RAID group in to LUNS that get assigned to one or more servers. Certain disks get carved up and assigned to certain hosts. Manual and static but very configurable and you know your performance characteristics.
FAST (the autotiering feature..not FAST Cache) can’t do this. You can’t take a LUN created manually and have it be tiered up to faster storage or down to slower storage automatically. FAST requires the concept of “pooling”. To use FAST we don’t create RAID Groups, we create Storage Pools. Pools are easy. They are great. You create a pool and then just throw disks in there. Say, 15 fibre channel disks, 5 EFDs, and 30 SATA disks. You then tell the array to carve up a LUN out of that pool. The array then figures out where to place the actual data. If it needs better performance it’ll move it to EFD. For slower it’ll go down to SATA.
But, what if you already have an array all carved up and you aren’t using storage pools? Your options are a bit limited and mainly include:
1. Buy more disks (if the array has room), assign those disks to a pool and then migrate existing LUNs to the pool.
2. Try to shuffle things around to free up disks to create the initial pool.
3. You don’t.
Also, if you have a CX or CX3 you can’t use the new FAST features until you replace the old array or do an in-place upgrade and move to newer CX4 storage processors.
So what I’m trying to get across is that it’s FAR easier to use FAST if you start on day 1. It can be very hard to move to it later unless you have available disks to put in the pools. If you do have available disks you can easily create the new autotiering pool and migrate existing LUNs to it.
One more thing… I’ve talked to a number of potential FAST users that thought this new autotiering required EFDs. It does not. It just needs two tiers of storage. You can easily autotier between SATA and Fibre Channel disks. No EFDs are required. It is highly suggested that all disks of the same type be the same speed. What I mean by that is that all FC drives in the same pool should be the same RPM. So make them all 15K RPM or 10K RPM. The reason for this is that the autotiering does not take RPM in to consideration with tiering so data may be spread across both drive types leading to inconsistent performance.