You receive an error: File <unspecified filename> is larger than the maximum size supported by datastore <unspecified datastore> when trying to backup a VM or any other process that involves a snapshot.
When disk 1 is 200 GB in size, on a datastore formatted with block size of 1 MB disk 2 is 300 GB in size, on a datastore formatted with a block size of 2 MB The error is occurring because the snapshot of disks cannot be created in the datastore due to file size limitations based on the blocksize of the datastore. We have seen this error occur when a VM has multiple disks on different datastores. For example:
When a snapshot is being created, by default all snapshots reside in the same datastore as its vmx configuration file (usually the same datastore as disk 1). New in vSphere, the snapshots now carry the same block size limitation as the disks - for a 1 MB blocksize, the maximum file size is 254 GB, for a 2 MB blocksize - 510 GB.
VMFS datastores can be created with different block sizes, resulting in different maximum VMDK sizes. A VM with multiple VMDKs on different datastores, formatted with different block sizes may result in datastore size errors when performing vRanger backups.
VMware Block Size Limitations: (VMFS3)
Block Size Largest VMDK/File Size
1 MB block size = 256 GB maximum filesize
2 MB block size = 512 GB maximum filesize
4 MB block size = 1024 GB maximum filesize
8 MB block size = 2048 GB maximum filesize
An example for a multi-VMDK VM:
VMDK1 (50GB) stored on a 1MB block size datastore (A)
VMDK2 (300GB) stored on a 2MB block size datastore (B)
Typically, the VM's .vmx file is located on the same datastore as the VM's 1st VMDK and the vRanger snapshots are stored on the
same datastore as the .vmx. Because a snapshot is created for each VMDK, the snapshot for VMDK2 would be stored on datastore (A).
As this snapshot would be larger than the block size limitation for datastore (A) an error condition is encountered.
There are 3 possible solutions:
1. If the larger disk does not need to be included in the Backup/Repolication it can be marked as Independent-Persistant.
2. Perform a VMware Storage vMotion to move the VMDK on the 1MB formatted datastore to another datastore with a larger block size.
References include VMware KBs 1004040 and 1005544.
3. Reformat the datastore. There is no way to change the block size of a VMFS datastore once it has been created. The datastore must be reformatted with the required block size.
This would require moving the VMs/VMDKs located on the datastore to another location, then reformatting the datastore.