Topic
2 replies Latest Post - ‏2013-05-23T06:07:16Z by ScaleoutSean
janfrode
janfrode
15 Posts
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Pinned topic GPFS on Storwize V7000, one or many LUNs?

‏2013-05-10T22:41:47Z |

We currently have a GPFS filesystem consisting of several 1-2 TB LUNs, for a total size of about 12 TB. Connected to 7 GPFS nodes. The reason we have lots of smaller LUNs is mostly historic, having been migrated from an older storage system. On the Storwize V7000 it seems a bit of hassle to do remote copy of many LUNs, so I'm wondering if we can get away with a single 12 TB LUN instead, or two 6 TB LUNs ?

Is there any performance reasons to go with many smaller LUNs, vs. one large on the V7000? On the storage side it will all be striped over the same physical disks in both cases....

  • gcorneau
    gcorneau
    141 Posts
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    Re: GPFS on Storwize V7000, one or many LUNs?

    ‏2013-05-13T14:41:50Z  in response to janfrode

    The most accurate answer is: maybe.

    Performance tuning and design involves many factors with GPFS, one of which is the number of LUNs configuration. 

    In general, we like to have multi-LUN GPFS file systems so that GPFS can queue up and execute multiple I/O operations in parallel from the operating system.  With a single LUN file system (or a single LUN per storage pool per file system) you don't give GPFS any ability to parallelize I/O prefetch/writebehind. 

    Of course, also in general, we don't like to have multiple GPFS file system LUNs over the same RAID group/rank in the storage because that can lead to lots of head movement as GPFS stripes it's data across the LUNs.  Again, in general, modern storage subsystems often have a lot of cache that help alleviate some of this penalty.

    Reality says that you should test both in your environment with a real (or representative) workload because that too, plays a part in determining the best layout.  Large block streaming I/O has different requirements from a LUN/storage perspective versus small block, random I/O.

  • ScaleoutSean
    ScaleoutSean
    4 Posts
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    Re: GPFS on Storwize V7000, one or many LUNs?

    ‏2013-05-23T06:07:16Z  in response to janfrode

    @gcorneau gave a good response, I'd only add that it doesn't sound like you have a lot of HDDs in the V7000.

    Based on that I wouldn't expect that a different setup would give you better performance. IMHO the V7000 has reasonably decent handling of consistency groups. Unless you're hitting some SAN, V7000 or other limit and really have to cut down on the number of LUNs, I would not change anything.