Close - but a couple of corrections:
You have two options for metaLUN expansions in a CLARiiON - striped and concatenated. Concatenated expansion takes a chunk of disk of any size and bungs it on the end of the existing LUN. Easy. You get the additional space immediately, and you can use space from the same RAID group as the existing LUN if you want with no performance impact. You must use disk of the same type (FC or SATA) and protection (either RAID protected or not) in a concatenated metaLUN.
A striped metaLUN is something you have to be more careful with. The individual components have to be the same size, RAID protection and disk type (FC or SATA)., As you note, you mustn't put two components on the same physical disks (same RAID group) or you'll end in a world of performance pain with spindle contention. The upside, though, is that if you plan your CLARiiON storage layout carefully, you can get some serious performance gains by using metaLUNs over multiple smaller RAID groups.
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by: CSGRPPosted on 2009-09-15 at 12:35:54ID: 25338455
Found answer I was looking for.
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1. if you have an existing stripped metaLUN that is using LUNs from a set of raid groups (one LUN from each raid group) - let call that group of raid groups a hyper-group to distinguish it from the other raid groups. If you then need to expand this metaLUN and the only space you have remaining is in this "hyper-group", then you can create one LUN in each raid group (make them all the same size) and then you can concatenate these new LUNs to the original metaLUN. By making the new LUNs the same size and then selecting each one when you concatenate, the array will first stripe these new LUNs together (they are all the same size) then it will concatenate this new stripped component to the original metaLUN. This way the performance of the new metaLUN will not increased or decreased.
2. if you stripe the new LUNs (say they were all the same size as the original LUNs in the metaLUN), then the performance of the metaLUN will be less - you get a condition called "vertically stripped" metaLUN - this is because the stripe is across all the LUNs - two from each raid group. You want to try to avoid this if possible - it's a performance hit.