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 2 possible solutions:
1. 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.
2. 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.
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