For incremental backup of virtual disk, always enable changed block tracking (CBT) before the first snapshot. When doing full restores of virtual disk, deactivate CBT for the duration of the restore. File-based restores affect change tracking, but disabling CBT is optional for partial restore (file level restore), except with SAN transport. CBT must be deactivated for SAN writes because of thin-provisioning and clear-lazy-zero operations.

Backup software should ignore independent disks (those not capable of snapshots). These virtual disks are unsuitable for backup. They throw an error if a snapshot is attempted on them.

When using VMware Tools debug logging with quiesced snapshots, do not log

vmtoolsd.data

to a local file on the VM, such as

C:\Temp\vmtoolsd.log

. Instead set

vmtoolsd.handler=vmx

to use the tools service.

To back up thick disk, the proxy's datastore must have at least as much free space as the maximum configured disk size for the backed-up virtual machine. Thick disk takes up all its allocated size in the datastore. To save space, you can choose thin-provisioned disk, which consumes only the space actually containing data.

If you do a full backup of lazy-zeroed thick disk with CBT deactivated, the software reads all sectors, converting data in empty (lazy-zero) sectors to actual zeros. Upon restore, this full backup data will produce eager-zeroed thick disk. This is one reason why VMware recommends enabling CBT before the first snapshot.

With CBT enabled for backups on an NFS datastore, thin-provisioned virtual disk may be turned thick upon restore, unless the NFS server supports

lseek(...SEEK_DATA)

,

ioctl(...FS_IOC_FIEMAP)

, or equivalent function.

Do not make verbatim copies of configuration files, which can change. For example, entries in the

.vmx

file point to the snapshot, not the base disk. The

.vmx

file contains virtual-machine specific information about current disks, and attempting to restore this information could fail. Instead use

PropertyCollector

and keep a record of the

ConfigInfo

structure.