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Has, or does, anyone use dm-cache - specifically for caching SAN based storage locally?

I'm looking for a way to speed up SAN based storage on a CentOS 5.6 + XEN Hypervisor which uses iSCSI mounted SAN storage. dm-cache seems like it do the trick, but I've never heard of it before until someone mentioned it in another mailing list. A quick search on google didn't really give me much in terms of actual user experience.

Does anyone use it? Any feedback? Pitfalls? Success stories?

I'm referring to this:

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After skimming the IBM Research Report about it I'm not convinced of its value. If a SAN is constructed properly the throughput and number of IOPS provided will dwarf a single (or a few) local disks.

I wish the authors would have run tests that were even close to real-life. Doesn't IBM have hardware? Instead they use an ISCSI SAN backed by a single spindle and we get his claim:

It is understood that some of the scalability issues ex- hibited by this iSCSI-based storage system can be at- tributed to the fact that a single disk is used to serve the concurrent client accesses. However, as demonstrated by the above experiments, the performance bottlenecks ap- pear even for a small number of clients. Therefore, it is reasonable to believe that the same issues will still per- sist for a better-equipped and more load-balanced stor- age system, when the number of clients is relatively lager than the current setup.

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