Replication job not using CBT

[Jimb0]

Hi

We are using Veeam replication to migrate to a new VMWare environment. On some of the jobs when I run an incremental sync I see the following message in the job details :

Cannot find dirty block information in the previous restore point, CBT will not be used

It's happening only to some VM's, usuually the larger ones. This is causing issues due to the time it is taking to perform each sync.

I have spoken to support who suggested that I try to run the CBT reset Powershell script which I have done, but it hasn't had any effect. Does anybody have any ideas as to the cause of the issue and how to fix it ?

Many thanks.

[Vitaliy S.]

Hi James,

CBT reset script should take effect only on the subsequent run, not right after you reset it, as it has to do the full pass first. If you don't see that happening that I would suggest looking into VMs config and check what prevents Veeam from using CBT data.

Thanks!

[Avshalom]

Hello,

I have a problem with one of our VMs, it has a successful daily backup on the main site, but at the replication job to the remote site, it's not using CBT with the message:
"Cannot find dirty block information in the previous restore point, CBT will not be used"

the job then is taking very long time, around 24 hours...
daily backup on the main site which uses CBT - takes around an hour

The Source VM Version is: 8
The CBT is enabled on all disks,
The VM Size is about 4.5TB

Any help?
Thanks

[Shestakov]

Hello Avshalom,
Is that the only VM with such a problem? Have you tried to reset CBT?
If you have associated support case number, please post it here.
Thanks!

[torteflo]

Hi,

same error here : "Cannot find dirty block information in the previous restore point, CBT will not be used"

CBT has been reset, same error now.

The VM is 17TB large (7,4TB used, thin provisionning).
I just create a new case at Veeam support (case id : 02302844).

Environment :
Production room
1 vcenter 6.5u1 (vCSA)
2 ESX 6.5u1
1 Veeam server VM (9.5u2)

DR room
2 ESX 6.5u1
1 physical Veeam proxy

1Gb link between both rooms, replicating over network (nbd).
It takes between 20min and 1hour to replicate when CBT run fine.. And days and days when it is failed!

Please help, if anyone can.

[foggy]

Please contact technical support for a closer look.

[torteflo]

Hi,
obviously already done as I gave the support case here.
Veeam support told me they don't see any error in logs, and so ask me to contact VMware support.
Which is already done too.

But I would like to have an explanation to why this message display, and what I can do to troubleshoot it.

[foggy]

Let's see what VMware support could advise. Could you please share your Veeam support case ID, btw?

[torteflo]

Hi,
already given in my first message : 02302844

[torteflo]

Hi,
we found out ourselves.
There must have been some bad data in the job's metadatas.
Deleting the existing replicas, creating a new job and executing a new full replication solve the issue for the next incremental sessions.
CBT is now up and running.

[djecak]

Hi all,

Recently I have cloned my replication job in order to create 2 new replication jobs. Just re-shuffled VMs between the jobs.
Now, every job and every VM gets the same message: "Cannot find dirty block information in the previous restore point, CBT will not be used"
No errors, just that message and the jobs are taking forever to finish because of digest calculations (no CBT).

Anybody experienced something similar before?

Thanks in advance!

[Vitaliy S.]

Hello,

Try to reset VM CBT data and if it doesn't help, then contacting our technical support team should be a way to go. Additionally, there are some suggestions above on how to fix it, but it requires full re-sync.

Thank you!