During my inquires which backup software will support vSphere 6.0 I came across BackupExec 2015 where I saw that vSphere 5.0 was no longer supported. This made me little bit confused because vSphere 5.0 is still supported by VMware until 2016/08/24. I ask via Twitter and got the following feedback in April:
@Fred_vBrain vSphere 5.0 is not supported by VMWare that is why we dropped support. We do support 5.1 and up. @davidstamen
— Backup Exec (@backupexec) April 6, 2015
Now I was more confused because VMware hasn’t dropped vSphere 5.0 support yet but few tweets later I got a link to the VDDK 6.0 release notes.
I read through it and come across the following paragraph I didn’t know until then:
VDDK 6.0 adds support for ESXi 6.0 and vCenter Server 6.0, and was tested for backward compatibility against vSphere 5.5 and 5.1.
I also checked previous VDDK (5.5) versions and found the following phrases:
The VMware policy concerning backward and forward compatibility is for VDDK to support N-2 and N+1 releases. In other words, VDDK 5.5 and all of its update releases support vSphere 5.0, 5.1, and 6.0 (except new features).
Conclusion
In general when using VMware VDDK you have a backward and forward compatibility to support N-2 and N+1 releases. When a backup software vendor is updating it’s version he can decide if he implements only the most recent VDDK or use different VDDKs for different platforms. In case of Symantec or IBM only VDDK 6.0 is used which means according to VDDK 6.0 release notes only vSphere 5.1, 5.5 (N-2) and 6.0 is supported. Veeam on the other hand supports vSphere 4.0 to 6.0 which leads me to the conclusion that they are using multiple VDDKs in their product to stay compatible with older hypervisor versions.
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