Live VMware datastore expansion with running VMs

How to enlarge datastore capacity in Virtual Center?

There are several ways to get more disk storage available for your VMs running on VMware ESX. Adding an extra datastore is an option, but having multiple datastores creates an extra administrative overhead since you now have multiple datastores to monitor.

Another option is to simply extend an existing datastore. Live!

The most important prerequisite is that this datastore cannot have the maximum capacity yet. Up to ESX version 5 this maximum is set to 2TB. So if you have a datastore of for example 525 GB, enlarging it to 700GB can be done by simply expanding the underlying LUN.

In my case I had to perform this trick on a VMware ESX 4.1.0 cluster and a 525 GB datastore, coming from an EMC VNX. The steps I had to take are very basic, but I’ll describe them to you anyway:

First you have to enlarge the LUN on the storage array. Take any precaution you have to take to do so. If the LUN is in a pool, simply right-click and “Expand” to enlarge the LUN. If the LUN is in a traditional RAID Group layout, you can consider creating a METALUN (striped or concatenated).

Anyway, you now enlarged the LUN and you want ESX to pick it up. In Virtual Center select an ESX host and in the upper right corner of the GUI click “rescan”.

dsexp1-Rescan-start

Select the datastore you want to grow and choose “properties”.

dsexp2-DS-properties

Now click the “increase” button.

dsexp3-DS-Increase-1

Verify that the datastore is indeed the LUN you’re seeing (size and LUN address) and press “next”.

dsexp4-DS-Increase-2

Confirm that the free space is now available and press “next” again.

is the extra capacity available?

Select the amount of free disk space you want to add to the existing datastore and press “next”.

dsexp6-DS-Increase-4

Now once again verify that you’re expanding the original size to the new size. Both values are on this confirmation screen. Press “finish” to actually start the expansion.

dsexp7-DS-Increase-5

You’ve now returned to the properties screen of this datastore, except that now the larger size is visible. If all went well all remaining ESX hosts will automatically start a rescan. If you’re in doubt whether this happened or not, simply press “rescan” in the upper right corner again.

dsexp8-DS-Increase-6

dsexp9-Rescan-endCheck if the running VMs are still running, but since this is a nondisruptive action, you should be fine here and your datastore is ready for more VMs or expansion of existing VMs.

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