A time ago i had to configure a W2012 R2 essentials server with storage spaces and 2 virtual disks. As the real disk count and the disks itself where not final at that time, i had to resort to the powershell way of configuring the virtual disks. The purpose was to create 2 virtual disks, one with parity and 3 columns, and one with a mirror layout (no special requirements - created with server manager), both thin provisioned.
In the final setup there would be 5 disks 2*8T, 1*4T and 2*3T. At the time of creating the first virtual disk, the 2*8T, 1*4T and 3 other disks (smaller disks that should be removed later) where available.
Because i thought i knew that 3 columns would give me the largest space (2* the 8T and the 3rd the rest of the disks), i specified the powershell command to use 3 columns and the 3 first disks to use (default storage spaces would use as many columns as it possibly can, which would restrict expanding later - more disks to add before picking up).
Everything seemed to work fine, however after removing the smaller disks and adding the 2*3T disks, they where picked up by the mirror virtual disk, but not by the parity virtual disk.
As a side note, i have another W2012 R2 server where a similar setup is made, but the 3 column parity disk was created (by the default tools - not powershell) when there where only 3 disks in the pool (2 larger and 1 small disk). I added later 1 extra disk, which was directly picked up by the virtual disk expanding its space significantly.
What is limiting the usage of the 2 3T disks in the virtual disk, is it because the virtual disk was created by the powershell command specifying the 3 disks at that moment to use, or is it because i need another disk to fulfill the 3 column constraint (note the previous paragraph where this seems not the case)?
Are there powershell commands or other tools that can solve my problem (if it is possible without recreating the disk) to get a 3 column parity disk with each column at least 8T (8T - 8T - 4+3+3T)?
Edit 20160606: I did some other tests creating a new virtual disk in powershell with 3 columns, without specifying the disks to use, and as I expected the software dit not choose wisely regarding future expansion: it selected the 2 smallest disks and one of the larger disks probably limiting the expansion later on with the available disks (I could replace disks, but enclosure space and available Sata ports are the current limits to the amount of disks that can be connected)