VMware: Creating a snapshot for a virtual machine fails with the error: File is larger than maximum file size supported (1012384)

When Creating a snapshot for a virtual machine fails

Or you receive the error:
File is larger than the maximum size supported by datastore

Note: This error does not occur on ESX 3.5 or earlier.

ESX 4.0 is able to detect when a snapshot file at maximum size cannot fit into a datastore. Instead of allowing the file to be created, which may not work correctly if it grows to big, ESX cancels the operation and displays the above error.

To confirm if the snapshot files may be too big, compare the size of the virtual machine’s base disks against the block size of the datastore which contains the virtual machine’s working directory.

Note: If you are using Raw Device Map, you should compare the size of the RDMs instead of the base disks.

Maximum file size on a datastore:

If you are still experiencing this error after confirming the snapshot files can fit on the datastore in question, proceed to Calculating the overhead required by snapshot files in this article.

To resolve this issue:

1. Select the virtual machine.
2. Click Edit Settings.
3. Click Options.
4. Click General.
5. Select Configuration Parameters.
6. Click Add Row.
7. Type workingDir under the Name column in the new row.
8. Type the directory on the new datastore with an appropriate block size in the Value column.
9. Perform a storage vMotion to an alternate datastore with a larger block size.

Alternatively, you can migrate the virtual machine while it is powered off (cold migration) to an alternate datastore with a larger block size.

Calculating the overhead required by snapshot files

The failure depends on the size of the virtual disk. All virtual machines having disks with a maximum supported size by VMFS may experience this error.

For example, a virtual machine with disk sized 256 GB stored on VMFS with 1MB block size fails to snapshot because of the additional overhead required for the delta files. Though the maximum file size for a 1MB block size is 256GB – 512, creating a vmfsSparse (delta) disk requires additional overhead space about 2GB. The resulting delta has potential to grow beyond the file system limit.

To resolve this issue, move the virtual machine to a VMFS volume with 2MB block size.

Overhead for the snapshot is roughly about 2GB for a disk size of 256GB. If snapshots are to be used, consider the overhead while deciding the size of the disks.

Additional Information

When performing a storage vMotion, you may encounter the error:

Moving a virtual machine that has snapshots is not supported when the virtual machine has disks placed outside of its home datastore.

Maximum file size per VMFS block size can be found in the ESX 3.x and 4.0 Configuration Maximums document.

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Daniel Buonocore

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