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Thursday, 8 September 2011

Veeam 5 - File is larger than the maximum size supported by datastore

When Veeam is used to back up a virtual machine a snapshot is created while the backup takes place.

By default VMware snapshots are stored on the same datastore as the virtual machine configuration file (the .vmx file).

So, if the VM that you want to back up has additional VMDK files on other datastores and the additional VMDK file is larger than the block size of the datastore where the configuration file is stored you will not be able to back it up with Veeam and you will get this error.

File <unspecified filename> is larger than the maximum size supported by datastore <unspecified datastore>

The datastore where the snapshot will be created does not have a large enough block size to hold the snapshot of the large VMDK so the operation fails.

To work around this you have two options:

  1. Storage VMotion the configuration file only to the datastore that holds the biggest VMDK for the machine in question.
  2. Edit the VMX file and reboot the VM.
If you have a licence for storage VMotion then simply do that as its simple and does not require a reboot, remember to use the advanced options for SVMotion to just move the configuration file.

If you don't have a SVMotion licence you will have to power off the VM and perform an offline SVMotion of the configuration file only.

Alternatively you can download the .vmx file using the VI Client and edit the "workingDir" entry to reflect a datastore with a large enough block size to accommodate the snapshot.

Remember that the .VMX file is read by the VM on startup so you will have to reboot it for the changes to take place, but if you have to reboot it why not just offline SVMotion the configuration file - it's much easier this way!

Once this is all done Veeam should back up your large VM again.