There are two things when you think of backup of virtual machines

• Application back which is called File Level Backup
• Entire VM back Image Level Backup, ( which is quite easy, cause you just need to back VMDK)

File Level Backup: It is recommended that you put all your data in Non-System Disk, it brings it's own advantages.

Backup Proxy Server is required for carrying out this task, this has been implemented especially to remove backup overheads from ESX/VM's. This would be Windows 2003 server, with Backup software installed(for example netbackup) which has VCB plugin to carry out the task.

COMPONENTS involved in VCB back process are:

• Hostd: On ESX Server and interacts with Virtual center
• VM to be backup:
• Backup Proxy server with 3rd party software installed on it.
• VCB Framework which consists of
  • vcbMounter
  • vLUN driver
  • Integration module
    • Pre & Post-backup scripts which ties with
  • Backup application (for example Netbackup)

VCB WORKFLOW:

• Backup application starts backup job as per pre-schedule time
• Pre-backup script is intiated by backup software 
  • Quiesces NTFS/FAT (only in case of MS Guest OS),this ensure no write operations are pending
  • Puts VM in snapshot mode
  • Snapshot is taken and put's VM into normal opertion
  • Backup software mounts this Snapshot for File Level Backup, and selected files are copied. (Done by Backup client)
  • For Image level back, entire disk is export to Backup proxy server.(Done by backup client)
• Post-backup script is called
  • which unmounts VM snapshot from backup proxy
  • Takes VM out of snapshot mode, commits any changes made to the disk during the snapshot mode.

Restoring backups done using VCB approach

Restoring file/Images taken via backup is not straight forward. There are three approaches for this

• Self-Service restore : Backup agent Installed on each and every VM
• Per-group restore : Select VM's which will do restore work (i.e. install backup agent only these VM's) and then get someone to restore files of those specific VM's
• Centralized restore: Backup agent is installed only on Backup Proxy and restore file/Image on backup proxy. After you can uses windows share to copy data over the location

These approachs differs from each other at one level i.e. present of backup agents. Backup agents here are only doing restore work.

For Image level backup you can use VCBMounter to backup entire virtual machine in the service console. VCBMounter quiesce the snapshot of the VM and export the setfiles which can be later on used to restore using VCBRestore. For file level back you have to use third party backup software. This can be done only from Service Console.