Monday, August 26, 2013

VMware snapshot files

VMware snapshot includes the following:

Virtual machine snapshot database file - vmsd:
 This is the snapshot database file, which is used by the snapshot manager to display the snapshot details, relations between the various parent/child snapshots etc. There will be one vmsd file created per virtual machine when a snapshot is taken
Virtual machine memory state - vmsn:
 This file is created when you select the option to snapshot virtual machine memory as well . One benefit of taking snapshot of memory is that it will let you revert to a snapshot with virtual machine in switched on state. If snapshot of memory is not taken, when you revert a snapshot the VM will go back to switched off state
Delta disks - delta.vmdk:
These are delta disks created when we take a snapshot. The point of time at which the snapshot is taken, the current disk is turned to read-only, and a delta disk is created for subsequent writes. A delta disk, like other vmdk files consist of two files. One descriptor file and one data file. Descriptor file will contain the details such as geometry and child-parent relation of the disk. The second disk will contain the actual data. The delta disk are made up of child disks or redo logs.It uses Copy-on-write(COW) mechanism for the purpose of saving space, ie only data that needs to be modified for a write are copied over. The unit of measure used by this disk is called a 'grain', default size being 64 KB

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