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I'm exploring Storage Pools in Windows Server 2016 and I'm trying to create one virtual disk that uses the entirety of the space available in the pool. However, it appears that it's not using all available space.

In my instance, I have 4x50Gb drives in the pool. However, when I issue a New-VirtualDisk -UseMaximumSize, the size of the drive is only 192 Gb. Why is it not able to use the remaining 8Gb?

Is there a way for me to see what the maximum available space in the pool is at any time? Applicable to the above but also, say for instance, I add more disks into the pool and would like to expand the virtual drive. How would I know the value to pass to Resize-VirtualDisk (annoyingly, there's no -UseMaximumSize parameter on that cmdlet)?

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During the creation of Storage Pool the Microsoft Storage Spaces using the maximum available size of the disks which can be added to the pool. The same for creating virtual disks in storage pool even without using "Maximum size" parameter. The thing is that your disks do not use exact 50 GB per disk, because:

"To a hard disk manufacturer, one KB is 1000 bytes, one MB is 1000 KB, and one GB is 1000 MB. Essentially, if a hard disk is advertised as 500GB, it contains 500 * 1000 * 1000 * 1000 = 500,000,000,000 bytes of space. The hard disk manufacturer thus advertises the disk as a 500 GB hard disk. However, Microsoft use groups of 1024. When you’re buying memory, a KB is 1024 bytes, a MB is 1024 KB, and a GB is 1024 MB. To work back from the 500,000,000,000 bytes above: 500,000,000,000 / (1024*1024*1024) = 465.66 GB

Keep in mind that the hard drive manufacturers are using the accurate description of the terms–the prefix giga, for instance, means a power of 1000, whereas the correct term for powers of 1024 is gibibyte, though it isn’t often used. Unfortunately, Windows has always calculated hard drives as powers of 1024 while hard drive manufacturers use powers of 1000."

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    I can see how that may come into play. In my case, each of the constituent drives measures 53687091200 bytes (as returned by get-physicaldisk) while the storage pool measures 211527139328 (as returned by get-storagepool). If my math is correct, the pool is short by 3221225472 (or 3 Gb) bytes. – Ben Thul Jul 25 '18 at 15:59

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