ID #1107

How to check if a snapshot is an orphan ?

 

How to check if a snapshot is an orphan ?

Platform : ESX , Workstation , Fusion


Scenario


Orphaned snapshots are snapshots that are not part of any existing snapshot-chain.
This should never happen - but in some cases ....

- unwise user action some time ago
- Workstation or ESX crash
- host OS crash or power-failure
- running out of diskspace during a snapshot action
- misconfigured or buggy behaviour of VMware tools like VCB or VDR
- misconfigured or buggy behaviour of third party backup tools - especially for ESX and ESXi


Checklist


It is not trivial to check if a snapshot is orphaned for several reasons
- looking at the snapshot number in the filename is unreliable
- looking at the vmsd file is unreliable
- looking at the filename hint in the vmx-file only references the last used one at the end of the chain
- a snapshot maybe used by a VM in a different directory
- a snapshot maybe part of a linked clone in a different directory
- a snapshot may be the only part of a a separete branch in the snapshot-tree

To be absolutely sure if this snapshot is orphaned and so can be deleted we have to check if it is referenced
by any of the other vmdk-descriptions found in the same directory.
In case any other vmdk references the snapshot it may be part of one branch of the tree.
In case the snapshot is a direct child of the basedisk it may be a valid separate branch all by itself.
In case the CID or parentCID of the snapshot are referenced by any other vmdk it may be a required snapshot even if the parentfile name hints don't match.

What is the size of the snapshot file ?
The larger it is the longer it has been in use - the more valuable data may be stored in it.
Even If it is very small it may have never been used but it also may contain a single file - maybe just THE important one.

Long story short: you have to make an educated guess after analysing the other vmdks in the same directory.


Warning !


Automated scripts that check for orphaned snapshots are only trustworthy if you can rule out user-mistakes.

 


Tags: find, howto, orphan, snapshot

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