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Size of DPM replica is much larger than Hyper-V VM size RRS feed

  • Question

  • For some of the Hyper-V virtual machines that we back up using DPM 2010, far more disk space is needed for the replica than we though it would.

    For example, one of these machines has two virtual hard disks, of which approximately 68 GB are used. The used replica size in DPM, however is 485 GB, i.e. seven times as much.

    We back up the VM twice per week, with a rentention time of 5 days. I.e. the replica are should never contain more than two snapshots of the virtual machine, i.e. the used size should never be more than twice of the used hard disk size.

    Is the following equation true? ("=" means "approximately equal")

          "used replica size" = "used hard disk size" * "number of retained replicas"

    If yes, how can I find out why DPM is using such an excessively large amount of disk space for the VM?


    • Edited by fmunkert Friday, August 31, 2012 6:11 AM
    Friday, August 31, 2012 6:09 AM

Answers

  • Hi,

    OK - so when the VM's were protected, co-location option was unchecked so each VM is on it's own replica.  When the VM's were initally protected, there is the opportunity to adjust the replica and recovery point volume sizes, could it be someone did the manual adjustment and fat fingered the allocation so it is now grossly overallocated ?    The only supported way out is to stop protection and delete replica and then re-protect and make sure the new allocation is correct. 

    NOTE: If you are using fixed size .VHD's - DPM will need to allocate the full size of the .VHD's - not just the used space inside the fixed .VHD files.


    Please remember to click “Mark as Answer” on the post that helps you, and to click “Unmark as Answer” if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread. Regards, Mike J. [MSFT] This posting is provided "AS IS" with no warranties, and confers no rights.


    Monday, September 3, 2012 6:41 PM
    Moderator

All replies

  • Hi,

    The default Hyper-V Co-located replica volume that DPM creates by default is 250GB meaning we will co-locate as many Hyper-V  guests that fit on that 250GB volume up to 8 before we create another 250GB volume.
    You can override the overall replica volume size in the GUI during protection.

    Depending on your average Hyper-V guest, you can modify that registry key so you can take better advantage of the co-location feature.

    Key name: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft Data Protection Manager\Collocation\HyperV
      Valuename= CollocatedReplicaSize and should be a multiple of 1GB  (1073741824 bytes)


    Key Name: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft Data Protection Manager\Collocation\HyperV
     ValueName= DSCollocationFactor  - this is the number of guests to co-locate per replica - default is 8


    Now, for you to do this, you would need to perform the following steps.

    1)  Calculate the average size HyperV  guest under protection, and plan for some growth over time.
    2) Multiply the (average size + growth) * 8  – this will be the new collocatedreplicaSize – make sure it’s a multiple of 1GB  (1073741824 bytes)
    3) Modify the registry key to make it that new value.
    4) Unprotect the  Hyper-V guests and chose the option to delete the replica volumes (yes that will remove all your backups, but the only way to get them on newly sized co-located replicas) - , be sure that you UNCHECK the option to delete tape recover points unless you want to expire them also.
    5) Re-protect the Hyper-V Guests, make sure the enable co-location checkbox is checked.
    6) DPM will make new specified sized replica volumes and co-locate up to 8 Guests per replica.


    Please remember to click “Mark as Answer” on the post that helps you, and to click “Unmark as Answer” if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread. Regards, Mike J. [MSFT] This posting is provided "AS IS" with no warranties, and confers no rights.


    Sunday, September 2, 2012 2:49 PM
    Moderator
  • Hi Mike,

    thanks for your detailled answer, but I do not see how it relates to my question. First, we do not use the tape co-location feature. Second, my question was about the size of the VM's replica, not about the size of the whole replica volume.

    Our DPM server management console displays a different replica size for each VM. If any co-location would be in effect, it would display the same size for a number of VMs, wouldn't it?


    • Edited by fmunkert Sunday, September 2, 2012 5:12 PM
    Sunday, September 2, 2012 5:11 PM
  • Hi,

    Run the below in a DPM powershell command window and see what it reveals.

    # Get datasource path for co-located data sources
    # Where protectiongroupname = the protection group you want to get information for.
    # Look for datasources that share the same replicapath

    $pg = get-protectiongroup (&hostname) | ? { $_.friendlyname -eq 'protectiongroup_name'}
    get-datasource $pg  | sort-object -property replicapath | ft replicapath, name, diskallocation -AutoSize


    Please remember to click “Mark as Answer” on the post that helps you, and to click “Unmark as Answer” if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread. Regards, Mike J. [MSFT] This posting is provided "AS IS" with no warranties, and confers no rights.

    Monday, September 3, 2012 5:18 PM
    Moderator
  • Hi,

    Run the below in a DPM powershell command window and see what it reveals.

    The command shows the same replica sizes as the DPM server management console. For most VMs, the replica size is approximately the same as the used hard disk size (as seen inside the VM using Windows Explorer). For some VMs, however, the replica size is much larger (up to seven times larger) than the hard disk size used by the VM.

    Each data source has a unique replica path.
    • Edited by fmunkert Monday, September 3, 2012 6:02 PM
    Monday, September 3, 2012 5:59 PM
  • Hi,

    OK - so when the VM's were protected, co-location option was unchecked so each VM is on it's own replica.  When the VM's were initally protected, there is the opportunity to adjust the replica and recovery point volume sizes, could it be someone did the manual adjustment and fat fingered the allocation so it is now grossly overallocated ?    The only supported way out is to stop protection and delete replica and then re-protect and make sure the new allocation is correct. 

    NOTE: If you are using fixed size .VHD's - DPM will need to allocate the full size of the .VHD's - not just the used space inside the fixed .VHD files.


    Please remember to click “Mark as Answer” on the post that helps you, and to click “Unmark as Answer” if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread. Regards, Mike J. [MSFT] This posting is provided "AS IS" with no warranties, and confers no rights.


    Monday, September 3, 2012 6:41 PM
    Moderator
  •   The only supported way out is to stop protection and delete replica and then re-protect and make sure the new allocation is correct. 

    I have tried that, but DPM uses approximately the same replica size as before.

    NOTE: If you are using fixed size .VHD's - DPM will need to allocate the full size of the .VHD's - not just the used space inside the fixed .VHD files.

    That is the answer! The affected VM's two hard disks have a total size 466 GB, which is pretty close to the actual used replica size of 485 GB.

    Tuesday, September 4, 2012 10:58 AM