The default action with VMware ESX(i) when applying a snapshot is to create the relevant snapshot files in the working directory of the virtual machine. In an environment using VMFS datastores with a single block size across all LUNs this works fine however; where datastores exist for specific applications requiring large VMDK files an issue can occur.

Scenario

datastore-1 formatted with 1mb block size for VMDKs < 256gb hosting a virtual machine ‘C:’ drive, circa 40gb.

datastore-2 formatted with 2mb block size for VMDKs > 256gb & < 512gb hosting a virtual machine ‘E:’ drive, circa 350gb.

VMware VCB or an administrator (in this case Mr Snappy) issues a snapshot.

Mr Snappy with the VMware Admin handbook

The snapshot will fail to apply and return an error to the VI client console or to VCB.

The resolution

A new datastore will need to be created and formatted with a block size equal to the datastore where the large VMDK file resides. Power down the guest operating system / virtual machine then add an additional line to the virtual machine VMX file, this being:

workingDir=”/vmfs/datastore-name/”

Finally, the virtual machine will require re-registering. Either remove it from the inventory then browse the datastore to add it back in or use the vmware-cmd -s at the command line. Whichever way you feel more comfortable with. If you’re not using the vMA but need the command line for ESXi see this article to get an SSH console.

Further reading can be found within VMware KB article 1002929.