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.
snapshots
Delete all snapshots
Today I encountered an old misunderstood principle again. A customer had created several snapshots on a virtual machine. Several… well to be exact 15. All snapshots were larger than 20GB. When the VMFS volume, on which this VM was located, ran out of diskspace he decided to use the button “Delete All”, but within a couple of minutes the VMFS volume ran out of diskspace again. What happened?
Situation:
Snapshot 1 – 20GB
Snapshot 2 – 10GB
Snapshot 3 – 30GB
When you choose “delete all” the following will happen:
- Snapshot 2 will grow to 40GB at most
- Snapshot 1 will grow to 60GB at most
- Snapshot 1 will be committed to the original VMDK
- All snapshot files are deleted
In other words: Snapshot 3 is merged into Snapshot 2, Snapshot 2 is merged into Snapshot 1, Snapshot 1 is merged into the original flat.vmdk and afterwards all snapshot files are deleted. This means that if you want to delete all snapshots at once you will need around 130GB of free diskspace. So think twice when you press the “delete all” button.