In my RSS reader I noticed a blog on VM/ETC about independent disks and VCB. The thing is, no snapshots are created when a disk is in independent/persistent mode. This can be a problem when you want to use VCB on all your disks. But this can also come in handy when you want to disable a specific disk from being picked up by VCB. For instance a Database server with a 1TB D: disk is probably not a candidate for for VCB in a normal situation. But when setting the D:\ disk in independent/persistent mode this disk will be skipped by VCB because it’s impossible to snapshot a disk that’s in this mode. This way you can dump the C:\ aka System partition and restore the VM in case of disaster recovery more easily.
As most of you know, when VMware Consolidated Backup dumps image level backups VCB only dumps used diskspace. Unfortunately for us VCB does this by checking at block level if it contains only zero’s or not. If it contains only zero’s the block is considered empty, but an Operating System doesn’t zero out the disk space that contained the files when a file is deleted. An Operating System only clears the pointers to these files. This is why you could have a disk with only 4GB of used space and a 6GB VCB dump. As of ESX 3.0.2 update 1 VMware reintroduced the shrink option in VMware Tools. Kind of a weird name “shrink” cause the vmdk doesn’t actually shrink, the unused space is just zeroed out.