VM full backup with limited space in VM Datastores

HI,

Oracle Linux isn't technically supported as a guest OS for VM backup i.e. the mapping of the files when using a mapped backup. Having said that, since its basically RHEL it might work. 

On the other hand, you're running Oracle on it so I guess most of the 6TB is the database, which you'll need to backup with an Oracle policy which means you'll need an agent inside the guest.

I would do a mapped VM backup of the OS drive, and exclude the other 2 drives (one is backup drive anyways) and then take the agent backup with Oracle. If you're lucky and your storage is supported by cloudpoint you can even take a snapshot backup of the oracle depending on your configuration.

I'm not sure what you think the problem is, but using a VMware policy type with the accelerator option enabled would be a great place to start.

The first backup will take some time due to the size of the VM, but subsequent backups should take a lot less time as only changed blocks will be backed up.
You might want to look at whether you need to take a backup of the VMDK that has the backup directory and if this is not needed, look at the VMDK exclusion options in the advanced VMWare options in the policy (you will need the SCSI controller & lun information for this).

If you are worried that taking the snapshot of the VM will cause problems, remember that a VMware snapshot simply freezes teh VMDK files and creates a transaction log files which capture all writes to the original VMDK (when the snapshot is deleted at the end of the backup, these updates are written back to the original VMDK). 
If you still think you will have a space issue, you can always configure the snapshot location for the VM to be on a datastore that does have adequate space.