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How to Troubleshoot Stuck Bitmap Syncs

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An administrator may experience VPG(s) enter bitmap sync and get stuck. This article helps troubleshoot such an issue.

Root Cause

Bitmap syncs are typically caused by:

  1. Following an environmental issue.
  2. Insufficient resources to maintain replication of the I/O load of the protected application.



  • The VPG is in a continuous Bitmap sync that never completes.
  • VPGs keep switching between Bitmap sync and ‘Meeting SLA’ state.
  • No new checkpoints are seen on the VPG.


Environment failures 

Check if the environment had any failures/issues during the time the bitmap sync started. You can do so by checking the following 

  1. Zerto event – navigate to the Zerto events and check when did the Bitmap sync started. 

  2. Identify the relevant protected and recovery hosts vis the Zerto UI. 

  3. Navigate to vcenter/SCVMM and locate the relevant hosts

  4. Navigate to the alerts/events and check rather not the environment suffered from a failure/event that caused the Bitmap sync to occur.  

Bandwidth Throttling

If Bandwidth or time-based Throttling are enabled, the throttling values might not be sufficient for the environment to perform replication and cause frequent bitmap syncs. Disabling the throttling feature may assist with re-occurring bitmap sync or in case bitmap syncs cannot be completed.
Navigate to the site settings and check rather or not you have Bandwidth Throttling enabled (for more information on Bandwidth regulation click here). If it is enabled, check rather or or not the value meets the minimum required bandwidth (for more information see how to identify the minimum required bandwidth).

Planned / Scheduled Tasks 

 If you notice that the Bitmap sync keep occurring during specific hours of the day, please check internally to see if there are scheduled operations (outside of Zerto) on the environment that may utilize network/storage resources (Scheduled backups, for example)

VRA resources

When the VRA’s CPU and memory are overloaded, the IO buffers can fill up and cause delays on the replication and therefore, a bitmap sync will occur. For more information, please see how to validate VRA resources.  If you identified that additional resources are required you can follow the KB Adding resources in Vmware.

Network Resources

To check if the network resources are causing the bottlenecks:

  1. Use iPerf tool to verify the bitrate available between the 2 sites. For more information on how to run iPerf please see - How to check bandwidth using iperf. 

  2. Compare the results by:

    1. Use the bandwidth output to verify if the bandwidth observed matches the configuration.

    2. If the values match, login to the ZVM UI and go to the dashboard page. There you can find the WAN graph which you can compare to the results of iPerf. 

Contact Support

If the issue persists, contact Zerto support and include the following information:

  1. Reference the KB

  2. Attach screenshots of the results of all of the steps that were taken (including iPerf, VRA resources, Screenshots, Etc.)

  3. Name of the the affected VPGs and their VRAs

  4. The following logs will be needed 

    1. Time frame - 8 Hours

    2. Relevant VPGs

    3. Relevant Sites

    4. Relevant VRAs

    5. Relevant hosts logs and hypervisor logs.

    6. If VCD is being used, VCD logs will be required as well.

  5. Collect the logs only after you’ve opened a case and have the case number.

** for more information please see How to collect Zerto logs**