Topic
3 replies Latest Post - ‏2012-10-08T16:09:33Z by SystemAdmin
Tstags
Tstags
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Pinned topic V7000 - Expand Storage Pool with Different Type Mdisk Array

‏2012-10-05T09:04:18Z |
Hi,

i have a Storage Pool made up of an MDisk composed by 6 x SAS 600 HDs.

Now i want to expand this Storage Pool with another Mdisk composed by 6 x SAS 900 HDs.

But when i create the Mdisk with the SAS 900 i can't expand the existing Storage Pool.

How can i do this?

Thank you very much
Updated on 2012-10-08T16:09:33Z at 2012-10-08T16:09:33Z by SystemAdmin
  • TMasteen
    TMasteen
    279 Posts
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    Re: V7000 - Expand Storage Pool with Different Type Mdisk Array

    ‏2012-10-05T19:38:57Z  in response to Tstags
    My advice: only use pools containing MDisks with similar performance characteristics. So create a new pool with the 6x SAS 900 drives.
    • Tstags
      Tstags
      4 Posts
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      Re: V7000 - Expand Storage Pool with Different Type Mdisk Array

      ‏2012-10-08T08:01:56Z  in response to TMasteen
      Yes, i know manual and best pratictes suggests doing pools with disk with similar performances,

      infact this disks are of the same models and type of the existing 6 x 600 (just different size).

      So according to manual i could do it. It seems to me that there is a limitation about disk type of different SIZE

      wich is not mentioned in the manual. So i wonder why can't i do a mixed sized storage pool?

      Moreover i can do a different Mdisk TYPES storage pool if i use an EXTERNAL storage, so i don't see

      a real motive why I can't do be a Mixed size SP (or even a mixed TYPE SP).

      I think a good thing would be to trigger a warning on the interface in the case of different types or sizes Mdisk,

      but it would be up to the user to make the choice of doing or not.

      BTW in this particular case the two mdisk would be the EXACT same performance. Just different size.

      Anyone IBM tech can write something about this?

      Thank you very much
      • SystemAdmin
        SystemAdmin
        4779 Posts
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        Re: V7000 - Expand Storage Pool with Different Type Mdisk Array

        ‏2012-10-08T16:09:33Z  in response to Tstags
        "BTW in this particular case the two mdisk would be the EXACT same performance. Just different size."

        That is part of your issue - disks of the same class that are different sizes do perform differently. The other issue is that the extents are striped across the mdisks and if you blend different mdisks sizes into an existing mdiskgrp, you're setting your IO up to be pigeon holed in the future, even if you do so with disks that are exactly the same.

        Just because you CAN mix different disk types with external disk doesn't mean that you should either. Warnings about doing what you are trying to do are VERY clear in the redbooks.