• This topic has 5 replies, 3 voices, and was last updated January 29, 2019 by Matthew C.

Force Sync VPG question

  • When we did some failover testing on a DB VPG we had one DB not come up correctly.  I was instructed to force sync the VPG and this corrected the issue.  Is it possible to do a force sync on a VPG as a scheduled task or can it only be done manually via the admin console?

    Hi Tom,

    Many years ago I discovered the same issue as you. A server would blue screen during a test failover. Turns out it was because at some point in history, a snapshot was taken before a software upgrade, the upgrade went south, so the machine was rolled back to that snapshot.

    The issue here is that Zerto has no visibility into the snapshot rollback. It has no idea that the blocks that it saw as written (and replicated those blocks) have been undone. That creates a condition where your VMDK files are forever out of sync. A force sync fixes this issue because it compares every block, so that fixed it for me.

    This could be what happened to you, or it could of been something else, but I thought it was worth mentioning my cause, in the event it could be the same as yours, and if not, it’s still worth noting as I feel it’s a big hole right now that people might not even know about.

    Ok so the reasoning for telling that whole story is, like you, I needed a way to automate a force sync. I figure I could script a way to monitor vCenter for any snapshot revert tasks (which I did) then if it detects that, execute a force sync on that VPG, which I was able to do using the Zerto commandlets.

    So to answer you question, yes, it’s entirely possible to script a force sync, then have a scheduled task to execute it. Just be aware, a force sync can take some time, during which time you are not logging new checkpoints so if you have a real DR event in the middle of a force-sync, you will have data loss.

    Hope that helps.

    Matthew,  I appreciate the reply.  Via the logs they were not able to tell what caused the the blocks to be out of sync.  This VPG in particular has 14 databases and yes the force sync did take about an hour to complete.  Right now the question was posed by management if we could schedule this.  So just trying to gather the feasibility versus the risk on doing this.

    Then in short, the answer is yes, it can be done.

    Matthew, can you share your script to force resync?

    Senior Virtualization Engineer

    Hi Enrique. As of version 6.5 Zerto automatically detects this condition, so a manual script is no longer necessary.

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