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HOW TO: Shrink a VMware Virtual Machine Disk (VMDK) in 15 minutes

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HOW TO: Shrink a VMware Virtual Machine Disk (VMDK) in 15 minutes

In my previous Experts Exchange Articles, most have featured Basic and Intermediate VMware and Virtualisation Topics.

If you would like to read my Basic VMware articles,  they are listed here for your convenience.  

During this series of articles VMware released VMware vSphere 5.5 and VMware vSphere Hypervisor ESXi 5.5. These articles are also applicable to VMware vSphere Hypervisor ESXi 5.x and 5.5. For consistency, I have used VMware vSphere Hypervisor ESXi 5.1 through this series.


Increasing the size of a VMware Virtual Machine Disk (VMDK) is straightforward, and is supported in the vSphere Client, by selecting the virtual hard disk, and increasing the size using the up arrow. or typing in a new value. Please see my previous Experts Exchange article:


Resize - VMDK.jpg
However, although there is a down arrow present, you cannot shrink the disk in this way, it's not supported. The only supported method of shrinking a VMware virtual machine disk (VMDK) is to use VMware vCenter Converter Standalone and create a virtual to virtual (V2V) conversion, a similar process to a Physical to Virtual (P2V) conversion.

Please see my previous Experts Exchange articles


V2V Disadvantages
V2V Conversions can be slow.
You need to ensure, you have enough datastore storage space for the new virtual machine disk.
The virtual machine is converted, so there is a small risk, the conversion can cause issues with the converted virtual machine.
The converted machine can contain a different MAC address.
V2V are prone to failure.

V2V Advantages
Support end-user method of re-sizing a virtual machine disk.
GUI Interface when using VMware vCenter Converter Standalone

After reading and understanding this article, you will be able to reduce the size of virtual machine disks in less than five minutes. I will let the reader decide if this is a faster method than the traditional practice of using a V2V, to change the size of a VMware Virtual Machine Disk (VMDK). On occasion we come across an installation, where an Administrator has assigned a 2TB virtual disk, and does not have the space to create a V2V!

In this article we will show you HOW TO: Shrink a VMware Virtual Machine Disk (VMDK) in 15 minutes

I feel this is a little more advanced, so I've not included it in the Basic VMware article series.

Before your start the following procedure, please ensure you have a valid and tested Full Backup of your virtual machine. This does not mean a VMware Snapshot.

Also check to see the virtual machine is NOT running on a Snapshot disk, If unsure please refer to my Experts Exchange Article


The following procedure is split into two parts

Shrink the Operating System partition - This is covered in Step 1.
Shrink the VMware Virtual Machine Disk (VMDK) - This is covered in Step 2

1. Login to the Virtual Machine and shrink the OS Partition

Before we can shrink the VMware virtual machine disk (VMDK), we need to shrink the OS partition. (to avoid file system corruption). In this example I am using Windows 2008 R2, which has a shrink function. If you are using another OS, please see the other 3rd party partition utilities which are available, they are listed in my Experts Exchange article Using an RDP (Remote Desktop Protocol) connection or connect via the Console, using the vSphere Client, login to the virtual machine as an Administrator.
Logon to the Virtual MachinePress Control-Alt-Delete to login to the virtual machine.
Right Click My Computer and Select ManageRight Click My Computer and Select Manage
Select Disk ManagementSelect Disk Management, and select the partition you need to shrink.
Right Click VolumeRight Click the Volume/Partition to shrink, and select Shrink.
Shrink Disk QueryThe above dialogue will briefly appear whilst the file system is queried.
Shrink C:the above dialogue will appear. Enter a size to reduce the OS partition.

In this example the VMware virtual machine disk (VMDK) is 40GB, and we would like to reduce the size of the VMware virtual machine disk (VMDK) to 20GB. The Disk Management utility scans the available file system, and reports a maximum size the OS partition can be reduce by, this is based on current file system usage.

Enter the figure 19.5 (GB) x 1024 = 19968
Shrink SizeOS Partition size after Shrink Operation.
Disk Manager after Shrink OperationAs can be clearly seen in the above screenshot, there is now an unallocated 19.5GB space on the virtual disk, in Step 2 the VMware virtual machine disk (VMDK) will be "chopped", removing this unallocated storage space, and finally reducing the virtual machine disk (VMDK) to 20GB. Providing that we DO NOT affect the existing partitions, this is a safe operation. So in effect the "cut" will be made in the unallocated storage space, after the OS partition.

2. Reducing the size of the VMware Virtual Machine Disk (VMDK)


Login and connect to the VMware vSphere Host ESXi server which hosts the virtual machine.

see my previous Experts Exchange articles


Power OFF the Virtual Machine, and change to the datastore path where the VMware virtual machine disk (VMDK) is located.

cd /vmfs/volumes/<datastore name>/<VM foldername>
VM Folder PathWe need to edit the *.vmdk, which is the descriptor file, which contains the variables for the size of the *.-flat.vmdk. Using cat, this is what the descriptor file contains
VMDK Descriptor fileThe number highlighted above, under the heading #Extent description, after the letters RW, defines the size of the VMware virtual disk (VMDK).

this number - 83886080, and it's calculated as follows:

40 GB = 40 * 1024 * 1024 * 1024 / 512  =  83886080

We wanted to reduce the size of the VMware virtual machine disk (VMDK) from 40 GB to 20 GB. So the value we need to enter into the descriptor file is:-

20 GB = 20 * 1024 * 1024 * 1024 / 512  =  41943040

Using vi, edit the descriptor file, and change the number from 83886080 to 41943040, and save the file.
VMDK Edited with viMigrate or Copy the virtual machine to another datastore, if you do not have the migrate option, see my Experts Exchange article here


After the virtual machine disk (VMDK) has been moved, you will notice the disk size reflects the desired size of 20GB.
Size of virtual disk, as viewed from vSphere ClientSize of virtual disk as viewed from consoleAfter restarting the virtual machine, and checking with Disk Management, you will notice the 19.5GB unallocated storage space, has been removed, and disappeared.
Size of virtual disk as viewed from Disk Management in the OS
Congratulations, you have successfully Shrunk a VMware Virtual Machine Disk (VMDK)

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Thank you for reading my article, please leave valuable feedback. If you liked my VMware article and would like to see more Articles from me, please click the Yes button near the: Was this article helpful? at the bottom of this article just below and to the right of this information. Thank You. Do not forget if you have a question about this article or another VMware, Virtualisation, Windows Server 2012 question, why not post a Question for me and the other Experts Exchange Experts in the VMware, Virtualisation, Windows 2008, Windows 2012 Zones. I look forward to hearing from you. - Andy :- twitter @einsteinagogo
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