Things you should know (TYSK) – vSphere 5.5 and VMDKs larger than 2TB

I had a recent conversation with one of my ex-colleague discussing about a problem he saw on a NFS datastore with VMDKs when he tries to extend it online beyond 2TB. I told him that this should work and he doesn’t need to take the VM offline to extend it. To be on the safe side I tried it in my homelab and got the following error message:

A specific parameter was not correct: Hot-extend was invoked with size (4369929010 sectors) >= 2TB. Hot-extend beyond or equal to 2TB is not supported. The disk extend operation failed: msg.disklib.INVAL

I tested it with a NFS and a VMFS datastore and got the same results. After a short research I found this KB article.
VMware introduced with vSphere 5.5 VMDK with 62TB but there are some limitations. Here are my most important take-aways from the KB mentioned above and I think a lot of people are not aware of that.

  • You cannot hot-extend a virtual disk if the capacity after extending the disk is equal to or greater than 2 TB. Only offline extension of GPT-partitioned disks beyond 2 TB is possible.
  • Fault Tolerance is not supported
  • Virtual SAN is not supported
  • Snapshots taken on VMDKs larger than 2 TB are now in Space Efficient Virtual Disk (SESPARSE) format
  • When using NFS, underlying filesystem must support large files (e.g. EXT3/4 -> 16TB, BTRFS/XFS -> 8EB, WAFL -> 16TB)
  • Maximum supported file size when using NFS is the lesser of 62TB and 1% less than the maximum file size supported by the NFS filesystem

For the other limitations please see the KB article.

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