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Due to processing by IBM, this request was reassigned to have the following updated attributes:
Brand - Servers and Systems Software
Product family - Storage
Product - IBM Storwize V7000, V5000 and V3000
For recording keeping, the previous attributes were:
Brand - Tivoli
Product family - Storage
Product - IBM Storwize V7000, V5000 and V3000
Since becoming aware of the undocumented 7-day averaging algorithm that easy tier uses, we need to take steps to mitigate the issues it causes with the limited SSD we have on our PureApplication Server racks. One of the things we are going to do is turn easy tier off for the management LUNs that are used by our software. We are doing this so that the SSD we have will always be available to customers for their running workloads. Moving forward, this is easy for us to do at MGEN (manufacturing) time for new racks, but we have an issue with existing racks in the field. I verified with John Lindley that for existing vdisk LUNs, if we turn easy tier off, easy tier no longer manages the extents and the vdisk extents are frozen in place. He mentioned that we could use migrateexts to move the extents where we want. We've tried migrateexts before and it resulted in an IO imbalance across our 3 HDD Mdisks, even though we moved the same number of extents from SSD to each of the 3 HDD arrays (I don't know of a way to know where the extents came from).
Not sure why easy tier works that way. I would have expected that when you turn easy tier off, it marks any extents currently on SSD as available to move off immediately. This is the enhancement we are requesting; if we turn Easy Tier off on a vdisk, we want a way to move any of its extents on SSD back to HDD. I had an email exchange regarding this with John Fairhurst. He stated "I think the function you want is to be able to pin a vdisk's extents to a particular tier but retain easy tier 3's performance-based balancing within the tier". John and Jian Ying Hu both mentioned the term "Easy Tier 3" to me as the next version of the Easy Tier code. Thanks.
You reference some function like Easy Tier 3 not already in the product. Furthermore, it's not clear when that function is available why you will no longer use Easy Tier for rebalancing pools. Please help make clear what exact enhancement you are requesting and for which existing function if appropriate. Thanks.