VMware Horizon Mirage client disk space requirements

Lately the question comes up how much disk space the Mirage client does require?

The VMware Horizon Mirage Installation Guide states: At least 5GB of free space

These 5GB of space are required for normal operation. Normal operation in Mirage terms are centralization and steady state uploads. For both operations the 5GB are required for VSS snapshots, manifest files and other Mirage data.

When it comes to base layer and app layer deployments the required disk space is higher of course. The reason is that you need space to save the data which is contained in the base layer or the app layer.

For example: You want to deploy Office 2013 as an app layer. Office 2013 requires around 3GB of disk space. In this case you need to have at least 8GB free disk space on the client to successfully deploy this application (layer).

5GB for the Mirage client + 3GB for Office 2013 = 8GB total required disk space

If Mirage is used for Windows 7 migrations the required disk space growth even further. When a Windows 7 migration is done with Mirage as first step the Windows 7 base layer and optionally some application layers (this is a new feature in Mirage 4.3) are downloaded to the client.

Example: Your Windows 7 base layer has around 25GB. Then you need at least 30GB of free space on the clients hard drive.

5GB for the Mirage client + 25GB for the Windows 7 base layer = 30GB total required disk space

If you deploy an application layer the same time you do the migration you require additional free disk space in the size of the application layer.

Another example: Your Windows 7 base layer has 25GB and you deploy Office 2013, which requires 3GB disk space, in the same process. Then you need 33GB of free disk space.

5GB for the Mirage client + 25GB for the Windows 7 base layer + 3GB for Office 2013 = 33GB total required disk space

After the Migration you are able to free a lot of disk space because, if the migration was successful, you can delete the Windows.old folder. The Windows.old folder is created during the migration process and contains a complete copy of the old Windows installation. The deletion of this folder can be easily automated, just follow the instructions in this knowledge base article: Removing the Windows.Old directory after User Profile or Windows 7 Migration with VMware Horizon Mirage

And now the disk space requirements for a restore operation. As a rule of thumb for a restore operation (e.g. disaster recovery, revert to old Windows version, hardware migration) you need as much disk space as it was occupied on the original system. This equates to the total size of the CVD which can be found in the CVD properties in the Mirage management console.


Example: So if your system drive contained 80GB of data you need 80GB free space in addition to the 5GB for the Mirage client.

5GB for the Mirage client + 80GB total CVD size = 85GB total free required disk space

Lastly we need to have a look at the disk space requirements for the driver library. The free disk space required for the driver library on the end point depends on the number of drivers you import and assign to a device using the driver profile/library.

For example if you download the Lenovo Windows 7 driver pack for the ThinkPad T430/T530 series and import it into the driver library as is you require around 1.5GB of free disk space. Incase of a Windows 7 migration using a base layer in the size of 25GB and a driver profile containing 1.5GB of drivers you required 26.5GB of free disk space plus the 5GB for the Mirage client.

5GB for the Mirage client + 25GB for the Windows 7 base layer + 1.5GB for the driver profile = 31,5GB total required disk space

The driver library ist applied automatically on operations such as centralization, migration, hardware migration and restore, base layer update and of course if you use the “Set driver library” option. So you should add the driver library every time you do a free disk space calculation like you would do for the 5GB required by the Mirage client.

If for some reason or another you end up not having enough free disk space on the client an event is logged in the Mirage management console.

As you can see the event log even shows you how many free space you have and how many is actually required to successfully finish the current operation.

All listed disk space requirements in this article are not exact and just estimates. The actual disk space required may vary based on the deduplication functionalities in Mirage. Anyway the numbers outline in this article should give you a good idea about the required disk space and most of the time the required disk space will be less.


8 thoughts on “VMware Horizon Mirage client disk space requirements

    1. Mirage will not check if there is enough disk space before the operation is started, in your case before assigning/provisioning a layer. But once you started the operation and it can’t be finished because there is not enough free disk space you will get a message in the Mirage event log.


  1. I checked my calculation about storage requirements at my current project (Tim, you know the customer 🙂 ).
    My calculation is the following:
    5GB Mirage Client + 10GB VSS + 20GB Windows 7 (our Base Image is about 23GB) = 35GB
    BUT important is that we always should think about the time after the Windows 7 migration. We can migrate with 35GB free disk space but the user needs much more space running Windows 7 in the future. So I add to this calculation 20-30GB to have peace about disk space for the next years… 
    I have a SQL script that give me a list with clients that have less than 35GB free disc space and about 70% of this users have VSS and/or I/O Problems reported at Mirage.
    So is there a difference between Win XP and Win 7 regarding storage usage? Would be interesting to know if the VSS works on a different way on Windows XP but I can´t find any information from MS.


    1. Hi Felix,

      Mirage requires at least 1GB of free disk space to successfully create a VSS snapshot. But from my understanding this is not the maximum size a VSS snapshot can grow. The maximum VSS snapshot size can grow up to a certain percentage of the size of your C partition. By default this is 12% on Windows XP and something between 2-5% on Windows 7. If you have a Win 7 C partition in the size of 60GB this would be around 1,8GB. The percentage can be configured by adjusting the disk space usage of the system protection feature.

      If there isn’t enough free space or the max. VSS allocation is reached there will be VSS errors because no snapshots can be created. The 5GB of free space we recommend in most cases should be enough but when there are many file changes and operations this may be not be the case.

      In regards to the free space for future growth: Good point but I think if you delete the Windows.old directory after the migration you should be on the save side.


  2. Hi Tim,
    what about the space required on the Mirage server side? There’s some tool to calculate it? Is a simple sum of CVD’s space or there’s a compression and dedupe on the repository as well.
    Thank’s a lot


    1. Unfortunately there is no good rule of thumb here because environments are just too different. I have seen CVD sizes from a few GB up to 40-50GB per CVD. Best thing to do is a pilot with around 10% of all clients and just centralise them. Than you have a good indication of the disk space required. For some very rough estimates we use 20GB per CVD but please do not size any productive environments with this size. It’s just to get a sizing idea.


  3. Hello I had a problem, I have not enough space on the machine with Windows XP, I require Migrating to Windows 7 , there is a method to use a removable drive instead of the C Drive: or download the necessary files from the base image in this unit. I really urgent response because I could not find documentation about it


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