Why can the setting size of storage space exceed the size of the storage pool it is in?

Question

The version of Windows I am using is: Windows11 23H2

Previously, I created a parity-based storage pool using four 2TB hard drives, and added a 7TB storage space to it. (as shown below)

Recently, I replaced all hard disks with 8TB drives, and the storage pool displayed 29.1TB (24.2 available) (as shown below).

I expanded the original 7TB storage space, but accidentally expanded it to 30TB when clicking on it, which exceeded the size of the storage pool.I wanted to adjust the size of the storage space, but the system informed me that it could only be increased and not decreased.Why can the storage space exceed the size of the storage pool it is located in?The excess capacity does not physically exist, so if files are stored, will they be lost?

Currently, there is no problem with using it, but the data I currently store is limited and does not reach 30TB. However, it is difficult for me to understand the logic. I believe that the storage space is based on the size of the storage pool in which it is located, and its size should not be larger than the storage pool.Also, the first image in the above figure shows that after I set the storage space to 30TB, why does the D drive still show 7TB?What does the maximum storage pool usage rate mean, and why do the values change between the two images I took at different time points?

In summary, my questions are as follows:

1. Why can the storage space exceed the size of the storage pool it is located in?
2. The excess capacity does not exist physically. Will there be any loss if files are stored?
3. After I set the storage space to 30TB, why does Drive D still show 7TB?

4.What does the maximum storage pool usage rate mean?

Answer 1

Hi,

1. Why can the storage space exceed the size of the storage pool it is located in?

The size of the storage space is the virtual disk size that you can see in Disk Management, which means you can write 30TB to the storage disk at most. Since the storage space is thin provisioned, not all the space is allocated in the storage pool when the storage space is created. In your case it's currently 4.84TB and it will increase as more data is written to the disk.

2. The excess capacity does not exist physically. Will there be any loss if files are stored?

If you run low on the available capacity of the storage pool, you will be informed by the OS so that you can simply add more disks to expand the storage pool and there is no need to modify the existing storage pool.

3. After I set the storage space to 30TB, why does Drive D still show 7TB?

Open Disk Management and see if there is any unallocated space on the storage space disk. If yes, right click on the D drive and select Extend Volume to add the unallocated space to the volume.

4. What does the maximum storage pool usage rate mean?

The resiliency type of the storage space is parity so you need additional space in the storage pool for resiliency.

Best Regards,

Ian Xue

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