Topic
5 replies Latest Post - ‏2015-01-14T19:19:12Z by benatnordisk
mandie
mandie
4 Posts
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Pinned topic What are the options for mirroring the PowerKVM host hard drive?

‏2014-07-03T10:54:26Z |

If the PowerKVM host is installed on a single HDD then this is potentially a single point of failure. What are the options for mirroring the storage that the host is installed upon? Presumably via a RAID card, but are there other options at the software layer through the hypervisor?

  • Brian_King
    Brian_King
    19 Posts
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    Re: What are the options for mirroring the PowerKVM host hard drive?

    ‏2014-07-03T12:56:31Z  in response to mandie

    All Power 8 systems come with support for hardware mirroring of the internal disk drives. Systems ordered with PowerKVM should be installed in manufacturing either to a single disk RAID 0 array or a two disk RAID 10 array. You can use iprconfig to display your current hardware RAID configuration. If you see a single disk RAID 0 array, you can perform a RAID array migration and seamlessly migrate the RAID array and all its contents to a RAID 10 array while the system is up and running. All you need is a second disk of similar capacity and of similar type. You can refer to the SAS reference guide for details on performing this RAID level migration:

    http://www-01.ibm.com/support/knowledgecenter/8247-22L/p8ebk/sasmigratingarrayslinux.htm?cp=8247-22L%2F0-3-10-5-3-5&lang=en

  • benatnordisk
    benatnordisk
    7 Posts
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    Re: What are the options for mirroring the PowerKVM host hard drive?

    ‏2015-01-14T02:24:30Z  in response to mandie

    Bringing this back up, I received a Power 8 system with PowerKVM pre-installed.  Oddly, ours has two raid cards, and two drives, one each on each controller.  Each is set up as a RAID 0 Array in iprconfig.  In PowerKVM, the first one (sda) is not configured to be mirrored to the second (sdb).

    Given that this is how it came from the factory, what was the intention here?  My guesses would be:

    A. we're supposed to use md to mirror it at the software layer

    B. The 2nd drive should be in a slot on the first controller, and hardware mirrored, and the config I received is an error

     

    My inclination is to move the 2nd drive to the first controller and mirror it there, but I'm just curious about what IBM's idea was here, and why the system was pre-loaded but mirroring not set up...

     

    Thanks in advance!

    • Brian_King
      Brian_King
      19 Posts
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      Re: What are the options for mirroring the PowerKVM host hard drive?

      ‏2015-01-14T15:29:07Z  in response to benatnordisk

      There are three RAID backplane options available on the Power 8 systems which support PowerKVM.

      #EL3T: PCIe3 x8 SAS RAID internal adapter 6Gb. This is a single, non caching, adapter.

      http://www-01.ibm.com/support/knowledgecenter/8247-22L/p8hcd/fcel3v.htm?lang=en

      #EL3V: Split backplane version of EL3T. Essentially two EL3T adapters, each sees half the disks

      #EL3U: PCIe3 x8 cache SAS RAID internal adapter 6Gb: Dual adapter RAID configuration configured in a multipath configuration, with both caching adapters seeing the same set of disks. dm-multipath must be used.

      The first thing to confirm is whether you have EL3V or EL3U. You can use iprconfig to check this:

      iprconfig -c show-ioas

      If the Product ID field shows "57D8001SISIOA", then you have #EL3U, if it shows "57D7001SISIOA", then you have #EL3V if there are two of them and #EL3T if there is only one shown.

      If you have EL3U, you can then simply delete the single disk RAID 0 array you are not using, and perform a RAID level migrate to two disk RAID 10, as described previously in this thread. If you have EL3V, and you want to mirror the disks, I'd recommend you first delete the single disk RAID 0 array you are not using, then use iprconfig to remove the disk from the system, then use iprconfig to add it back to the system, plugging it into a slot which is underneath the other adapter. Here are some links to help guide you through the RAID delete, hot remove, hot add process:

       

      http://www-01.ibm.com/support/knowledgecenter/8247-22L/p8ebk/delete_array.htm?cp=8247-22L%2F0-3-10-5-3-3-1

      http://www-01.ibm.com/support/knowledgecenter/8247-22L/p8ebk/remove_disk.htm?cp=8247-22L%2F0-3-10-5-5-7-0

      http://www-01.ibm.com/support/knowledgecenter/8247-22L/p8ebk/install_disk.htm?cp=8247-22L%2F0-3-10-5-5-7-1

      http://www-01.ibm.com/support/knowledgecenter/8247-22L/p8ebk/sasmigratingarrayslinux.htm?cp=8247-22L%2F0-3-10-5-3-5

       

      As far as your question of what was the intention here from a manufacturing process perspective, all systems coming preloaded with PowerKVM are installed to a single disk RAID 0 array. For customers desiring redundancy of their KVM host, RAID level migration is a simple way to obtain this without having to reinstall the host. We are likely to enhance this process in the future to install to a two disk RAID 10 array, as long as the system has two disks in it. If your system has EL3V, the split backplane design is intended to allow for either two separate PowerVM LPARs to be installed to the host, such as two VIOSes, or could also be used by a PowerKVM host and PCI passthru to pass the second adapter direct to a guest VM for access to fast local storage.

      • benatnordisk
        benatnordisk
        7 Posts
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        Re: What are the options for mirroring the PowerKVM host hard drive?

        ‏2015-01-14T19:19:12Z  in response to Brian_King

        Thanks for your reply!

        I have the #EL3V.  I suppose one could do a Linux md mirror of the two raid0 arrays, then it'd be able to tolerate a raid card failure too, but I opted for hardware raid, and moved both disks to the first controller and migrated to raid 10.

         

        Thanks!

         

  • ERYY_Faruk_Vahora
    ERYY_Faruk_Vahora
    16 Posts
    ACCEPTED ANSWER

    Re: What are the options for mirroring the PowerKVM host hard drive?

    ‏2015-01-14T14:55:59Z  in response to mandie

    Brian i sright. In my case, I am starting from scratch. First two drive with RAID10 for PowerKVM and ISO repository. Other 5 drives as RAID5 and i drive HS.

    I can share my install document when done but not sure when it will be available. Work in progress.

    May be I  will try migration as Brian pointed out for exisitng raid0 so I don't need to reinstall PowerKVM.

    Thanks.