Provisioned Size, Defined Size of a datastore explained

Last night I had to explain to Server admins as to what all the terms meant by Provisioned size, defined size and used size.

Let me first define the terms of what is Provisioned Size, Defined Size and Used Size is;

We will then better understand what is the situation right now and plus how we should calculate the growth of the disk.

Provisioned Size: Allocated space for (Defined Size at the creation of vm + Overhead + Snapshots)

Defined Size: Is the size we allocate at the creation of the virtual machine

Used Size: Actual used space from the defined space

Since the virtual machines have been defined to use as thin disks it allows us to over allocate space than the space that we have on the datastore.

In this example although we have 300GB datastore, we are able to allocate 532GB for disks using thin provisioning.

vm	Provisioned Size	Defined Size	Used Size
Vm1	102.05	100	14.43
Vm2	156.19	152	68.75
Vm3	46.05	40	16.73
Vm4	88.05	80	63.86
Vm5	84.05	80	39.36
Vm6	84.05	80	39.21
Total	560.44	532	242.34

When we are calculating the the storage we should calculate the defined size and add 25% on top of that for snapshots and overheads.

That’s VMware’s recommendation.