Virtual Disk API Programming Guide - Documentation - VMware

Virtual Disk Programming Guide
Best Practices for Backup
See “Tips and Best Practices” on page 81.
Backup and Recovery Example
The VMware vSphere API method queryChangedDiskArea returns a list of disk sectors that changed between
an existing snapshot, and some previous time identified by a change ID.
The queryChangedDiskAreas method takes four arguments, including a snapshot reference and a change ID.
It returns a list of disk sectors that changed between the time indicated by the change ID and the time of the
snapshot. If you specify change ID as * (star), queryChangedDiskAreas returns a list of allocated disk sectors
so your backup can skip the unallocated sectors of sparse virtual disk.
Suppose that you create an initial backup at time T1. Later at time T2 you take an incremental backup, and
another incremental backup at time T3. (You could use differential backups instead of incremental backups,
which would trade off greater backup time and bandwidth for shorter restore time.)
For the full backup at time T1:
1 Keep a record of the virtual machine configuration, VirtualMachineConfigInfo.
2 Create a snapshot of the virtual machine, naming it snapshot_T1.
3 Obtain the change ID for each virtual disk in the snapshot, changeId_T1 (per VMDK).
4 Back up the sectors returned by queryChangedDiskAreas(..."*"), avoiding unallocated disk.
5 Delete snapshot_T1, keeping a record of changeId_T1 along with lots of backed‐up data.
For the incremental backup at time T2:
1 Create a snapshot of the virtual machine, naming it snapshot_T2.
2 Obtain the change ID for each virtual disk in the snapshot, changeId_T2 (per VMDK).
3 Back up the sectors returned by queryChangedDiskAreas(snapshot_T2,... changeId_T1).
4 Delete snapshot_T2, keeping a record of changeId_T2 along with backed‐up data.
For the incremental backup at time T3:
1 Create a snapshot of the virtual machine, naming it snapshot_T3.
At time T3 you can no longer obtain a list of changes between T1 and T2.
2 Obtain the change ID for each virtual disk in the snapshot, changeId_T3 (per VMDK).
3 Back up the sectors returned by queryChangedDiskAreas(snapshot_T3,... changeId_T2).
A differential backup could be done with queryChangedDiskAreas(snapshot_T3,... changeId_T1).
4 Delete snapshot_T3, keeping a record of changeId_T3 along with backed‐up data.
For a disaster recovery at time T4:
1 Create a new virtual machine with no guest operating system installed, using configuration parameters
you previously saved from VirtualMachineConfigInfo. You do not need to format the virtual disks,
because restored data includes formatting information.
2 Restore data from the backup at time T3. Keep track of which disk sectors you restore.
3 Restore data from the incremental backup at time T2, skipping any sectors already recovered.
With differential backup, you can skip copying the T2 backup.
4 Restore data from the full backup at time T1, skipping any sectors already recovered. The reason for
working backwards is to get the newest data while avoiding unnecessary data copying.
5 Power on the recovered virtual machine.
40 VMware, Inc.