Changed Block Tracking (CBT) with multiple backups destinations and software types

[MCCS201110141]

Dear All,

i am testing multiple software versions that can use Changed Block Tracking (CBT).

CBT=(http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=102012...)

- VDR

- Veeam

- Acronis VMProtect (not sure if it uses it)

and i was wondering when you run multiple backups of a single VM that uses CBT that the backup application will fetch the correct change blocks for its backup.

as i understand from CBT that a backup application will fetch with a funciton a list of changed block sinds the last snapshot. so if another snapshot was taken, and the list was retrieved by another backup application will then the new backup fetch the correct blocks?!?!

as i read there are no real answers, i did read another post that talks about it : http://communities.vmware.com/message/1550818#1550818

i would be strange if it would not work.. could anyone explain how the usage of CBT would work with multiple vendors sofwtare or backups of 1 VM to different destnations.

Thanks in advance

[a_p_]

First you need to understand that CBT is a function of the VMkernel (ESXi) and not the backup software. From how I understand this, ESXi maintains a mapping table (the ctk files) which covers each data block of the virtual disk (the .vmdk file). Once a data block is modified, the time stamp of the modification is written to the according location in the ctk's mapping table. At the time a backup application runs, it requests the list of data blocks with a higher time stamp than the one of the last backup.

André