Hi dkmartin,

In essence that is correct, but there are a number of caveats - as I said earlier if you have tiered storage and depending on how it is configured things change.

If we take an example of a single LUN it is likely to be sliced up along the lines of what you expect usage to be with with a single slice assigned to each VG, you have to bear in mind that this single LUN may be accross many spindles at the back end - this is invisible to the system.

As an example in our VNX which has three tiers of disk at the end of the 8*16Gb agregated fibres (4 on fabric A and 4 on Fabric B) the breakdown of the system build is 30Tb of SSD for tier 1, 90Tb of 15K RPM SAS for tier 2 and 120Tb of SATA for tier 3. This has been carved into disk groups which are then sub-divided into LUN's, however the ratio of disk 1:3:4 assigned to each LUN and the intelligence of the VNX means that the parts of the system experiencing sgnificant I/O are moved dynamically to the tier 1 disk allocated to that particular LUN.

Each of the disk groups mentioned above comprises a number of physical disks, strangely enough in the 1:3:4 ratio for SSD, SAS and SATA generally twenty something disks given the sizes of the disks in the VNX.

So following the logic of your 1Tb Lun you would have available 125Gb of SSD that you do not have to manage, the system does it for you. It may well be that the storage technology you have is much older and that it does not thave this functionallity, in that case you'll have to provide a bit more information about the setup.

Regards

Gull04