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Maximum Number of Extents RRS feed

  • Question

  • I'm wondering if I should be concerned about the number of extents that are on 5 of my DPM 2012 SP1 servers: DPM01 (918 extents); DPM02 (867 extents), DPM03 (863 extents), DPM04 (721 extents) and DPM05 (643 extents).
    Monday, December 2, 2013 7:08 PM

Answers

  • Hi,

    Windows Logical disk manager (LDM) will use LDM records as follows:

    1 for the machines group record.
    1 record for every dynamic disk in the system.
    3 records for every volume created, plus one extra record for each extension of a volume.

    Each DPM server supports protecting 300 data sources, so as an example if you have a DPM server with 4 dynamic disks in the storage pool and are protecting the maximum 300 data sources, that would be 600 Volumes and assuming no extensions, the LDM record count would be 1+4+(600*3) = 1805.

    If you run the find.exe command as posted earlier, you can see how many LDM records are in use on the DPM server, look for the latest entry based on date / time.

    SAMPLE OUTPUT
    ===========
    10618,21:18:31 04-13-2010,0x0B88,0x0970,13,ReplicaAreaSetManager.cs,94,0x00000000,"Updated LDM cache; nMaxLdmEntries=[2960], nCurrLdmEntries=[59]",{00000000-0000-0000-0000-000000000000},8
    10619,21:18:31 04-13-2010,0x0B88,0x0970,13,ReplicaAreaSetManager.cs,245,0x00000000,"CheckLdmOccupancy returned [LdmOccupancyWithinLimits]; CurrentOccupancy=[0%], LdmWarningThreshold=[75%], LdmErrorThreshold=[90%]",{00000000-0000-0000-0000-000000000000},8

    DPM will warn you when 75% of the LDM records are used which will be at 2220.
    DPM will Block further extensions or new volume creation at 90% which is 2664 used records.


    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.


    Tuesday, December 17, 2013 11:15 PM
    Moderator

All replies

  • Hi,

    The number of extents itself does not necessarily mean much, but rather the total number of LDM records in use.

    You can check to see the number and percentage used by running this command against the DPM logs in the temp folder under the DPM installation location.

    find.exe /i "Ldm" msdpm*.errlog


    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.

    Tuesday, December 3, 2013 12:03 AM
    Moderator
  • What is the maximum number of LDM records permitted in DPM 2012 SP1?

    The following post stated that the maximum is 2960 records:

    http://blogs.technet.com/b/dpm/archive/2011/06/06/how-to-use-and-troubleshoot-the-auto-heal-features-in-dpm-2010.aspx

    Friday, December 13, 2013 7:08 PM
  • Mike Jacquet: Would you have a comment on this or could you point me in the right direction as to what forum I could post this to?  Thank you. - Jenna
    Monday, December 16, 2013 7:32 PM
  • Hi,

    Windows Logical disk manager (LDM) will use LDM records as follows:

    1 for the machines group record.
    1 record for every dynamic disk in the system.
    3 records for every volume created, plus one extra record for each extension of a volume.

    Each DPM server supports protecting 300 data sources, so as an example if you have a DPM server with 4 dynamic disks in the storage pool and are protecting the maximum 300 data sources, that would be 600 Volumes and assuming no extensions, the LDM record count would be 1+4+(600*3) = 1805.

    If you run the find.exe command as posted earlier, you can see how many LDM records are in use on the DPM server, look for the latest entry based on date / time.

    SAMPLE OUTPUT
    ===========
    10618,21:18:31 04-13-2010,0x0B88,0x0970,13,ReplicaAreaSetManager.cs,94,0x00000000,"Updated LDM cache; nMaxLdmEntries=[2960], nCurrLdmEntries=[59]",{00000000-0000-0000-0000-000000000000},8
    10619,21:18:31 04-13-2010,0x0B88,0x0970,13,ReplicaAreaSetManager.cs,245,0x00000000,"CheckLdmOccupancy returned [LdmOccupancyWithinLimits]; CurrentOccupancy=[0%], LdmWarningThreshold=[75%], LdmErrorThreshold=[90%]",{00000000-0000-0000-0000-000000000000},8

    DPM will warn you when 75% of the LDM records are used which will be at 2220.
    DPM will Block further extensions or new volume creation at 90% which is 2664 used records.


    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.


    Tuesday, December 17, 2013 11:15 PM
    Moderator
  • Mike: Thank you.  This was an incredibly simple explanation of how this process works.

    One additional question, how does using the "Shrink" option for decreasing the recovery point allocated volume size affect the LDM database?  Does it add a record to LDM or might it reduce one or more records in LDM?

    Wednesday, December 18, 2013 7:48 PM
  • Hi,

    Shrinking a DPM recovery point volume has the "potential" of reclaiming one or more LDM records.

    Lets take this example:

    Original recovery point volume (extent-1) was 50GB and DPM auto-grew it 4 times.

    extent-1 covers 0-50GB
    extent-2 covers 51-62GB
    extent-3 covers 63-77GB
    extent-4 covers 78-96GB
    extent-5 covers 97-120GB

    Now you reduce your retention period and wait for the older recovery points to get pruned at midnight and then run the shrink command.  Lets say we were able to shrink the volume down to the size of 65GB. Windows would be able to delete the last two extents (4 and 5) so you would re-claim 2 LDM records.


    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.


    Wednesday, December 18, 2013 8:13 PM
    Moderator
  • Mike: Thank you for your work on this forum.  This is very clear.  Nice nice explanation.
    Thursday, December 19, 2013 1:16 PM
  • Mike Jacquet,

    How often can/should Shrink be run on a recovery point volume? Are there any other details about when and when not to use Shrink?

    This blog post says "Repeated small shrinks cause free space fragmentation and increases the number of extents."

    http://blogs.technet.com/b/dpm/archive/2010/03/31/how-much-can-i-shrink-recovery-point-volumes-with-dpm2010.aspx

    In what scenario would Shrink actually increase the number of extents? And how does that correlate with your comments about Shrink potentially reducing the extents?

    -Taylorbox

    Thursday, December 19, 2013 5:42 PM
  • Hi,

    I would use shrink as sparingly as possible as shrinking volumes can lead to "free space" fragmentation and actually cause more harm than good.  When windows needs to create a volume, or extend an existing volume, it does so by finding free space on the dynamic disk(s).  If over time, you have shrunk lots of volumes slivers at a time, what you end up with lots of free space but scattered all over the disk.   Now instead of using a single LDM record to create a new volumes extent of lets say 50GB,  Windows disk management may need to piece together five 10GB slivers which will consume 5 LDM records.


    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.

    Thursday, December 19, 2013 5:54 PM
    Moderator
  • Interesting. So does this same "free space" fragmentation issue apply on DPM servers that frequently create and delete backups? Even if we never use Shrink, but the removed volumes are located all throughout the dynamic disk, would this lead to the same scattered free space issue? Would newly created volumes sometimes piece together slivers of free disk space instead of contiguous free space, and thus use multiple LDM records?


    • Edited by Taylorbox Friday, December 20, 2013 3:32 AM
    Friday, December 20, 2013 3:30 AM
  • Hi,

    Yes, any time volumes are deleted the space they occupied on the disk(s) then becomes free space that can be re-used for new volumes or existing volume extensions.


    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.

    Friday, December 20, 2013 3:01 PM
    Moderator
  • Good to know. Thanks for the explanation.

    Friday, December 20, 2013 10:09 PM