mount: unknown file system type 'VMFS_volume_member'

VMFS(Virtual Machine File System) is a clustered filesystem designed to store virtual machine disks for VMware ESX or ESXi Server hosts.

To access the data in VMFS drive.

• 1st boot your server using live Ubuntu, then
• Install vmfs-tools. (vmfs-tools is available in Ubuntu Software Center.) Or use command in terminal

sudo apt-get install vmfs-tools

or read manual install vmfs-tools from this link

Then mount vmfs drive

Use vmfs-tools to mount VMFS filesystem

1st find your vmfs drive using fdisk in terminal

use command in terminal

sudo fdisk -l

For example if you want to mount /dev/sdd1

1st create mount point 

mkdir /mnt/sdd
sudo vmfs-fuse /dev/sdd1 /mnt/sdd

Now you access your mount drive using

cd /mnt/sdd

For more Help Click Here

To Upgrade Datastores to VMFS-6 Click Here

That's it...