Resetting CBT on a replica - conflicting info

[dcolpitts]

So I've got an Exchange 2013 server (Windows Server 2012 R2) that I'm replicating between two sites over a 25Mbps link (there are other VMs being replicated too, but this issue is specific to the Exchange server). The Exchange consistently complains with every replication it can not find the dirty block information in the previous restore point, so CBT will not be used. This results in the replica taking 2 3/4 hrs every run (while other servers with larger disk and more daily change take 15 minutes due to the use of CBT). The ESXi hosts at both source and target are 6.0.0.10719132, and I'm using 9.5 Update 3a (9.5.0.1922) with both WAN Accelerators being HP Proliant DL380 Gen9 servers (24 cores and 128GB RAM each - so lots of horse power) running Windows Server 2012 R2.

I'm trying to determine the exact steps I need to take with replicas to reset the CBT on the replica. I'm assuming it is on the replica that I need to reset it, but I haven't found a KB yet that details CBT resets specifically with replicas. That said, https://www.veeam.com/kb1113 references two separate VMware KBs:

• https://kb.vmware.com/s/article/2139574
  https://kb.vmware.com/s/article/2048201

VMware KB2139574 specifically says "ensure the virtual machine is not running on snapshots". "If there are snapshots present, consolidate them to commit the changes." KB2139574 then further references https://kb.vmware.com/s/article/2003638 which explains how to right click a VM, and select Consolidate.

However VMware KB2048201 specifically states that step 2 is to "Remove any existing virtual machine snapshots."

Now maybe I'm missing reading, or misunderstanding, but it seems to me these two KBs conflict each other. One says to reset CBT on a VM with snapshots, you just need to consolidate it. The other says you need to delete the snapshots. And on top of that, kb1113 doesn't provide any details if there are any additional steps required for CBT resets on replicas.

So can someone from Veeam either point me to a Veeam KB that details resetting CBT for replica VMs or explain to me the steps that need taken here. Do I delete all the restore points or not before I reset the CBT on the replica? If I do delete them all, what needs done in the VBR console to accommodate this so the next replication doesn't puke?

Thanks

dcc

[Alex Uryumtsev]

Hi, Dean.

I've discussed your topic with our tech team. You should apply this kb article to your source VM.

After that changes replication job is supposed to work without any issues with CBT enabled function.

Please let me know how this worked out for you.

If you have any questions left, don't hesitate to ask.

BR,
Alex

[dcolpitts]

So Alex - just to confirm - I delete all my restore points, and VBR should not have any issues with that... If this is the case, you really should update kb1113 to specifically mention this for replicas.

dcc

[Alex Uryumtsev]

Yes Dean, don't hesitate to delete your restore points.

Thanks for your feedback, I will share it with our support team, so they will fix the kb article.

BR,
Alex

[dcolpitts]

Ok - I can confirm that resetting the CBT on the replicas as per VMware KB2048201 (https://kb.vmware.com/s/article/2048201), which in turn references VMware KB1031873 (https://kb.vmware.com/s/article/1031873) does appear to resolve my issue on some of the replica VMs. But even after two or three job runs after resetting the CBT, the CBT data is still invalid.

Also - I found PowerShell to be the quickest way to reset the CBT (code as per VMware KB1031873).

Code: Select all

connect-viserver -server vcenter01.fqdn

$vm="virtual_machine_to_reset"
$vmtest = Get-vm $vm| get-view
$vmConfigSpec = New-Object VMware.Vim.VirtualMachineConfigSpec

#disable ctk
$vmConfigSpec.changeTrackingEnabled = $false
$vmtest.reconfigVM($vmConfigSpec)
$snap=New-Snapshot $vm -Name "Disable CBT"
$snap | Remove-Snapshot -confirm:$false

# enable ctk
$vmConfigSpec.changeTrackingEnabled = $true
$vmtest.reconfigVM($vmConfigSpec)
$snap=New-Snapshot $vm -Name "Enable CBT"
$snap | Remove-Snapshot -confirm:$false

dcc

[Alex Uryumtsev]

I see. Then if these kbs doesn't resolve your case I would suggest you to contact our support team, so they can do deep dive into your logs.

Please, let me know about your results after investigation of our support team.

BR,
Alex