is it possible to make more than one Tier from external Storage on VSP with Hitachy Dynamic Tiering?
For example if I would have diskless VSP and two kind of external storage - will it be possible to tier between them with HDT?
Yes it is. Through HDT, you can have up to three tier's and all of them can be external storage if you chose. When creating the HDT pools, you will rank the external storage to indicate which external array is high, medium, or low performance creating your tier levels. All external tiers are ranked lower then internal tiers in an HDT pool for performance meaning external storage will always be a lower tier than internal tiers.
Worst think in HDT is . . .
If You have internat drive and external situation is like Brandon Lambert wrote - external always is lower tier.
It is not good if you have external flash storage like IBM Flash System.
In this case you can do good tiering within external storage or . . . I don't know is that supporting, but You can to loop - internal volume do as external with loop cable from normal port to external port. Then you have internal volume's as external .
I only heard about this. Somebody know is it supporting in HDS?
Jan Cipra, VSP does support external storage virtualization. As mentioned by Brandon, you can define 3 Tiers.
Just to add one more thing, when using external (or even internal) storage for any tier, don’t forget the HDT sizing rules still apply.
For example. An account had measured their Tier 3 external storage needing an average of 5% of the total IOPS required, so it was sized accordingly. What they forgot was that most of the time it was < 5%, but a few times it hit 15%. At 15% with HDT’s use of Cache Mode = Enable, that write rate sometimes put all LUNs on all application on the whole VSP into Emergency Destage Mode, effectively killing all performance on the entire subsystem until it could catch up to normal write caching levels.
Therefore, don't overestimate the performance of what the external storage can do, no matter how little you think it will be used or what the average percentage will be.
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