Netbackup VmWare restore change VMDK hash

Hello,

NetBackup calls VMware to initiate snapshot creation of the backed up VM, so maybe this step writes some metadata into VMDK header. However to confirm this is a question for some VMware guru rather than for NetBackup forum.

regards

M.

Yes, it is normal for the VMDK hash to change after a NetBackup backup. This is because NetBackup uses a process called deduplication to compress the backup data. Deduplication works by identifying duplicate blocks of data and storing them only once. This can significantly reduce the size of the backup data, but it also means that the hash of the VMDK file will change after the backup.

When NetBackup restores a VMDK file, it first checks the hash of the file to see if it has been deduplicated. If the file has been deduplicated, NetBackup will restore the deduplicated blocks of data from the backup media. This means that the hash of the VMDK file will be different after the restore.

Here is a brief overview of how NetBackup performs the recovery of a VMware machine:

1. NetBackup identifies the VMDK files that need to be restored.
2. NetBackup checks the hash of each VMDK file to see if it has been deduplicated.
3. If the VMDK file has been deduplicated, NetBackup restores the deduplicated blocks of data from the backup media.
4. If the VMDK file has not been deduplicated, NetBackup restores the entire file from the backup media.
5. NetBackup mounts the VMDK files on a VMware datastore.
6. NetBackup creates a new virtual machine from the mounted VMDK files.

The process of restoring a VMware machine from a NetBackup backup is relatively straightforward. However, it is important to understand that the hash of the VMDK files may change after the restore, due to the deduplication process.

I hope this explanation is helpful. Let me know if you have any other questions.

Was the restore of the VM successful? i.e. it ended with status 0?

Did you automatically start the VM after restore?

Hello guys,

you are confusing two different hashes. While rfm_columbia is talking about client side data hash (something like get-filehash on VMDK I suppose), meuhassan is mentioning deduplication hashing used on backup server side. One is file-level, another one is block-level, both have different vendors/purposes etc.

Check my post above, I suppose it is a clue. rfm_columbia  try to calculate VMDK hashes for these different cases: VM is without snapshot, VM with a snapshot, and VM is after Revert from snapshot which is comparable to restore from NetBackup. 

Regards

Michal