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Why does DPM server send tens of MB of data to DPMRA.exe client when beginning synchronization? RRS feed

  • Question

  • Consider this test:

    Remote Laptop

     - connected to DPM server over a WAN VPN

     - DPM Remote Agent (DPMRA.exe) installed

     - The only protected items are approximately 13 GB of user data 

     - Protected user data consists of a combination of a few small files from 500kB to 40MB, a 3GB iso, and a 5GB flat file.

     - Protected items were initially syncronized over LAN

    DPM Server

     - DPM 2012 R2 with colocated SQL Server 

     - Windows Server 2012 R2 Hyper-V Guest

    The Test

    1. Make any change to the contents of the 5GB flat file, for example, changing the value of one byte.

    2. Initiate Syncronization.

    3. Measure the amount of data sent from the DPM server to the DPM client. (Important: The opposite direction you'd think the data should go to be backed up.)

    My Results

    For this test, I measured approximately 13MB sent from the DPM server to the DPM client.  When I increased the flat file from 5GB to 10GB, that measured value increased to 40MB.

    This seems like a rather large amplification of data transfer (1 byte changing precipitates tens of MB transferred). 

    The Question

    Why does this happen?  How can I avoid it for large flat files?

    Tuesday, March 11, 2014 6:22 PM

All replies

  • Hi,

    Client protection does not use filter driver do track block level changes. Instead dpmra.exe does a block by block comparison between protected data on client and copy of the data on the dpm server. The data transferred includes the agent communications during crc comparison even if no data changed.


    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, March 13, 2014 4:34 AM
    Moderator
  • Thanks for the reply Mark,

    That explains it.  Could you confirm the following for me so I can work around this with confidence:

    1. For which files, exactly, is the CRC sent from the DPM server to the DPMRA.exe client?  All protected files?  Does it depend on file system modification date?  Or does it depend on bits in the contents of the file changing?

    2. How can I estimate the size of the the CRC sent from the DPM server to the DPMRA.exe client?  It doesn't seem to be linear with file size.  That is, a 5GB file seemed to cause 13MB transfer, while a 10GB file seemed to cause a 40MB transfer.

    Thanks,

    Alex

    Thursday, March 13, 2014 5:41 PM
  • Hi,

    Agent uses a combination of the USN journal, and ntfs metadata to determine which files have changed since the last synch, then agents do a block level comparison of file data only for files that have changed. The more files that are under protection the more metadata that needs compared which is included in Mb transferred size during synchronizations.


    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, March 13, 2014 10:50 PM
    Moderator