Full disks are read during incremental backup

[filippoAdb]

Case ID: #07206575
Backup job on vmware of 4 linux vm
CBT enabled, synthetic full once a week on Friday

Sometimes the backup job is very slow because the entire disks are read on one or more vm. It happened twice in the last 20 days, both times on Monday.
Some log details when it works as expected:
VM size: 1,3 TB (102,5 GB used)
Hard disk 1 (100 GB) 2,2 GB read at 103 MB/s [CBT]
Hard disk 2 (300 GB) 0 B read at 0 KB/s [CBT]

The corresponding log entries when the entire disks are read:
VM size: 1,3 TB (101,3 GB used)
Hard disk 2 (300 GB) 295,9 GB read at 56 MB/s [CBT]
Hard disk 1 (100 GB) 62,8 GB read at 56 MB/s [CBT]

Is there an explanation for this behavior ? Besides I wonder why unused disk space is read too.

[david.domask]

Hi @filippoAdb,

Big reads on incremental backups may be indicative of something interfering with the CBT data on the VMware side -- typically this can be either something resetting the CBT, performing backups when there were previously snapshots that you later consolidate, etc.

I see that the Engineer had asked for clarification on a few details, and they'll review the debug logs with the information you provided, and hopefully help narrow down the cause of this behavior for you.

As for unused space not being excluded, this is a function of our Bitlooker technology, and note there are a few limitations: https://helpcenter.veeam.com/docs/backu ... -exclusion

Please continue to work with Support as they research the behavior from the debug logs.