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WIndows Server 10 Volume Replica Log VolumeSize RRS feed

  • Question

  • When choosing the log disk for a Volume Replica, what is the recommended size? I suppose this log only starts to grow if the mirror cannot actively replicate, or if it falls behind during asynchronous replication? What happens if the log disk fills up?

    David A. Bermingham, MVP, Senior Technical Evangelist, SIOS Technology Corp

    Friday, October 3, 2014 5:22 PM

Answers

  • This is an extremely complex question and in the Technical Preview version of SR, we don't have this well covered. The log needs to be large enough to contain the write IOs from the source data disk without constantly wrapping prior to transmission to and acknowledgement from the destination server's log, which will lead to an expensive reconciliation called bitmap recovery.

    Basically, in Tech Preview, each IO will end up in a 2MB message - but many IOs may be aggregated into that same buffer, or maybe not, depending on how fast they are coming and the application you are using that writes them in the first place. So for instance, if you averaged 1000 write IOs a second and we were so incredibly inefficient that they only got one log message apiece (very unlikely), your 2GB log would wrap every second. If your destination server is not able to process all of that every second, you'd wrap and recover.

    The best way to tune the log size in Technical Preview is through the Storage Replication and Logical Disk performance counters and the WVR event logs, by looking at IO writes, SR data sent and received, and events indicating the logs wrapped and went into recovery. Or just make the log big and not worry about it because this is only for eval purposes.

    Note: In Technical Preview, if you want to create a log more than 31GB, you must apply this registry value before you configure replication:

    Windows Registry Editor Version 5.00

    [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\wvrf]

    "LMFS"=hex(b):80,1f,00,00,00,00,00,00

    Having fun yet? :) It's complicated and we understand that better than anyone - we are working hard to make this easier. Technical Previews are for the brave.

    For more recommendations and prerequisites, review my answers here: http://social.technet.microsoft.com/Forums/windowsserver/en-US/f843291f-6dd8-4a78-be17-ef92262c158d/getting-started-with-windows-volume-replication?forum=WinServerPreview&prof=required


    Ned Pyle [MSFT] | Sr. Program Manager | Windows Server



    Saturday, October 4, 2014 12:53 AM

All replies

  • This is an extremely complex question and in the Technical Preview version of SR, we don't have this well covered. The log needs to be large enough to contain the write IOs from the source data disk without constantly wrapping prior to transmission to and acknowledgement from the destination server's log, which will lead to an expensive reconciliation called bitmap recovery.

    Basically, in Tech Preview, each IO will end up in a 2MB message - but many IOs may be aggregated into that same buffer, or maybe not, depending on how fast they are coming and the application you are using that writes them in the first place. So for instance, if you averaged 1000 write IOs a second and we were so incredibly inefficient that they only got one log message apiece (very unlikely), your 2GB log would wrap every second. If your destination server is not able to process all of that every second, you'd wrap and recover.

    The best way to tune the log size in Technical Preview is through the Storage Replication and Logical Disk performance counters and the WVR event logs, by looking at IO writes, SR data sent and received, and events indicating the logs wrapped and went into recovery. Or just make the log big and not worry about it because this is only for eval purposes.

    Note: In Technical Preview, if you want to create a log more than 31GB, you must apply this registry value before you configure replication:

    Windows Registry Editor Version 5.00

    [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\wvrf]

    "LMFS"=hex(b):80,1f,00,00,00,00,00,00

    Having fun yet? :) It's complicated and we understand that better than anyone - we are working hard to make this easier. Technical Previews are for the brave.

    For more recommendations and prerequisites, review my answers here: http://social.technet.microsoft.com/Forums/windowsserver/en-US/f843291f-6dd8-4a78-be17-ef92262c158d/getting-started-with-windows-volume-replication?forum=WinServerPreview&prof=required


    Ned Pyle [MSFT] | Sr. Program Manager | Windows Server



    Saturday, October 4, 2014 12:53 AM
  • Appreciate the detailed response!

    David A. Bermingham, MVP, Senior Technical Evangelist, SIOS Technology Corp

    Saturday, October 4, 2014 3:05 AM
  • thank you. The fog thins out more and more.
    Saturday, October 4, 2014 11:59 AM