Block based incremental sync job completes with warning "SwitchToServerSync"

  • 7009379
  • 16-Sep-2011
  • 21-Aug-2013


PlateSpin Forge/Protect


When running block-based incremental synchronization jobs, the job completes with warning “SwitchToServerSync” at data transfer step.


Platespin block-based driver adds an upper filter to each volume on source workload. This filter monitors volume changes and maintains the record of changes in a bitmap file. Issue described above occurs when the block driver fails to get block changes from bitmap file and has to use MD5 checksum for comparing block changes on source and target volumes. This can happen due to multiple reasons as listed below:


  1. Changes to source volumes since it was last discovered (during add workload). If the volume id changes or volume is added or removed from source workload, the block driver will fail to monitor changes to volumes as the upper filter won’t be present on all volumes. To check for any volume changes, run “mountvol” command on source to view the list of volumes and compare it to volume information in source XML.

  2. Block driver is not added to all volumes as upper filter due to corrupted driver installation. Run “devcon stack storage/volume” command to check if block driver is added to each volume as upper filter.

    Note: Devcon tool can be downloaded from Microsoft KB 311272
  3. Corrupt bitmap file or old bitmap file (from previous block driver installation) is present on source. When block driver is installed again, it will not create a new bitmap file but continue to use the old bitmap file.


In order to resolve this issue caused due to any of the above mentioned causes, the block driver needs to be uninstalled and any existing bitmap files need to be deleted from source workload. Once previous installation and bitmap files are removed, reboot source and re-add workload. Block driver will be installed during next prepare of replication job or first replication/server sync job as configured. Verify the block driver is added as upper filter to all volumes on source by running “devcon” tool.

Steps to remove BBT driver from source are discussed in TID 7005616