Virtualization Pro

Nov 17 2008   5:22PM GMT

VMFS volume names: UUID and symbolic



Posted by: Eric Siebert
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Eric Siebert
VirtualCenter
VMFS
VMware
VMware ESX
VMware ESXi

If you have ever done a directory listing of your VMFS volumes on a VMware ESX host from the Service Console or using a file browser application like WinSCP you will notice the names of your VMFS volumes but also a number of directories that consist of a long string of numbers and letters as seen below.

VMFS Volume Listing in WinSCP

If you look in these directories the contents of them are exactly the same as the directories that are named the same as your VMFS volumes. So what are these directories? Let’s explain what happens when you create a VMFS volume to find out.

When creating VMFS volumes you are prompted to name them. This name is not what the ESX host uses to reference the volume; it is purely a friendly name to make it easier for the user to identify the volume. The ESX host actually uses a unique identifier called a Universal Unique ID (UUID) to reference the volume. The name you specify when you create a VMFS volume is a user-defined device name which is a symbolic link to the UUID of the VMFS volume. This is done to solve the problem of changing the device name, when you change the volume name you are only changing the user-defined device name and not the UUID of the volume. So when you look in your /vmfs/volumes directory you will see both a UUID, ie. 4404e8b4-bcfd52fc-1e4b-0017a4a91076 and the symbolic link, i.e. ServerA-Local. Changing to the symbolic link name by using the cd command or clicking on it in WinSCP simply takes you to the UUID directory. You can see the relationship between symbolic links and UUID’s by using the ls –l command inside the service console as shown below.

VMFS Volume Listing in the ESX Service Console

Additionally you can see the UUID of a volume in the VMware Infrastructure Client by selecting a volume in the Configuration, Storage section and then looking in the Details pane at the Location field. It’s definitely a lot easier to remember the volumes friendly name then it’s long UUID which is why symbolic links are used with ESX.

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