Thursday, April 23, 2015

Is it possible to have a directly attached SHARED Storage (accessed at block level) other than SAN or NAS?



We need storage specifically for HPC Lustre failover setup, where it is must that two servers should share same block level storage to have failover configuration.




With very limited knowledge on hardware, I have the below understanding:




  • NAS can be used for shared storage, but there will be bottleneck for
    speed due to intermediate network.

  • SAN can be used, but it is costly to implement the solution and
    not really needed for Storage of 50-100TB.

  • If at all we find multiple iscsi ports to the storage enclosure,
    the storage can be used only by splitting i.e., works as two

    storage devices and the same storage can't be used by both the
    systems. (And one thing to remind here, in the lustre setup, both
    the servers would be only attached, but only one will be used
    (not sure, how it is possible, again need to check on this).

  • Having two virtual machines may be how we can do it. But, then, it is
    not really helpful for the purpose of failover, as the physical
    machine would be only one.



But, while posting the question, I am thinking, may be we can compromise on speed in NAS, if we try having one directly attached server (primary) and the other attached via network (failover), so we face slowness only when the primary stops working.


Answer




Michael is saying that lustre does not care. All you need for lustre is for a block device that appears in /dev.



You still need to pay attention to the other layers, e.g network. You will loose performance if your network links are slower than your disks. This will likely be the case over ethernet. You will also loose a small amount using iscsi rather than direct attach even with fast links. Its hard to really guess what will be your issues since it depends on your hardware. I think that's why its difficult to get or give a clear answer (I have seen your lustre discuss post, but I think this is a question related more generally to hardware and interconnects).



Sean


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