VMware Backups are larger than expected, but usually smaller than the VMDK size.

Problem

VMware Backups are larger than expected, but usually smaller than the VMDK size.

Error Message

N/A

Cause

i.  The VM OS may consist of a filesystem type that does not support excluding deleted blocks.

Currently, the "Exclude Deleted Blocks" optimization option supports the following file systems: Windows NTFS, and Linux ext2, ext3, and ext4.

For filesystems not having the support for the mentioned optimization, NetBackup is only able to make use of the Changed Block Tracking (CBT) information received from VMware and optimize backup size accordingly.

For Thick Eager Zeroed provisioned VMDK's using XFS filesystem, VMware returns the whole provisioned disk space as a single change area extent in the CBT information, resulting in a Full Backup of the entire provisioned space.

ii.  Change Block Tracking(CBT) information from VMware may be reported incorrectly.

iii. CBT does not work with virtual machines residing on NFS. QueryChangedDiskAreas("*") returns an error when run against NFS version 3 and earlier.

Solution

• For Thick Eager Zeroed disks / XFS filesystem, VMware have stated that the solution is to use thin provisioned disks.
  
  For other cases where thick eager zeroed / XFS filesystem is not used, consider the following points.
   
• Reset CBT - should any corruption occur, this can lead to the entire provisioned space being backed up.
• Ensure VM's reside on VMFS data stores.
• If Virtual Machines reside on NFS, ensure NFS version 4 or above is used.

Reference:
https://www.veritas.com/support/en_US/doc/21902280-127283730-0/v62458922-127283730