Step By Step: How To Extend and Resize A Two-Way Mirrored Storage Tiered Space? #StorageSpaces #WS2012R2

4 min read

Hello folks,

A few blogs ago, I showed you step by step on how to create a Two-Way mirrored Storage Space, and how to replace a failed disk and repair the storage space.

In today’s blog post, I will walk through how to extend and resize an existing Two-Way mirror Storage Space and volume.

First things first, we need to check the current status of the existing virtual disk before doing any changes.

Let’s open PowerShell and get the existing virtual disk information:


As you can see, we have a mirror storage space with 363GB SSD Tier and 2.2TB HDD Tier, but we don’t have any remaining space to extend the existing volume.


The current volume “D” has 2.53TB of disk space and 1TB of free size remaining.

In my demo, I will add 1TB to the HDD Tier, as a side note, the same will apply if you are resizing the SSD tier as well.

Now before we start increasing the pool capacity and resizing the virtual disk, you have to pay a close attention on how many physical disks you can add to your existing storage space?

The answer to that question, it depends on what options were chosen when the virtual disk was initially created.

Let’s consider the following example:

You have a storage pool which has a 2-column, two-way mirror space. The two-column, two-way mirror space suggests you expand the pool capacity in sets of four disks for mirror spaces, in other words you have to multiple the number of columns by the number of copies, and since we have 2 columns, we need at least four physical disks.

Another thing to remember is, that after adding disks to the pool, there is no rebalancing mechanism. So the existing disks will be filled up first, before data is written to the added disks. That’s why the amount of columns must be chosen carefully at the time you created a virtual disk, because you can’t change the number of columns once the virtual disk is created.

With Get-VirtualDisk you can find many things about a virtual disk that you’ve created within a storage pool.


Since I am running a two-way mirror space with one column, I will add 2 X 1TB HDD into my JBOD.


Next, we will add the newly added disks to the existing Storage Pool, and then set the media type to HDD.



Let’s see now the maximum capacity that we can add to the storage tier and extend the existing volume.


As you can see, we can add roughly 1.1TB.

Here is another important point to remember: When you are resizing the storage space, you have to specify the new total size, and not the amount you want to increase, so in my example above, the existing Storage Space for HDD tier is 2,232GB, I need to add 1,116GB (new) + 2,232GB (existing) = 3,348GB total HDD tier, this of course if I need to add the whole capacity otherwise. The same concept will apply if you are resizing the SSD tier.

Let’s proceed and add the whole capacity.



Last but not least, we need to extend the existing partition which extends the volume “D” as well, and finally confirm the changes.




Microsoft has a great Storage Spaces Overview which goes in more detail and is well worth a read.

Hopefully the above notes and screenshots illustrate how you can extend and resize a storage pool when you have a need to do so.

Until next time… Enjoy your day!

About Charbel Nemnom 576 Articles
Charbel Nemnom is a Cloud Architect, Swiss Certified ICT Security Expert, Microsoft Most Valuable Professional (MVP), and Microsoft Certified Trainer (MCT), totally fan of the latest's IT platform solutions, accomplished hands-on technical professional with over 17 years of broad IT Infrastructure experience serving on and guiding technical teams to optimize the performance of mission-critical enterprise systems. Excellent communicator is adept at identifying business needs and bridging the gap between functional groups and technology to foster targeted and innovative IT project development. Well respected by peers through demonstrating passion for technology and performance improvement. Extensive practical knowledge of complex systems builds, network design, business continuity, and cloud security.

1 Comment

  1. Hi Charbel,
    awesome article. your explanations and pictures really paint a good picture. Thanks for sharing this information.

    I have a home LAB setup with Windows storage Spaces. planning on expanding the mirror by adding an External SAS storage enclosure.

    Thanks for the information again.

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