Server 2012r2 - Storage Spaces Mirror using mixed capacity disks

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Ben S

New Member
Oct 25, 2018
Hi, I've created a Storage pool containing 6 SATA disks connected directly to ports in my motherboard. I decided on a 3-column, two-way Mirror of and creating a simple volume (basically just wanted a resilient NAS Server with fast sequential R/W speed capable of theoretically coming close to saturating a 4Gbps bonded connection). I came to this column count because I happened to have 3 pairs of each capacity drive I used in the pool. This is how it breaks down:

2x 1TB drives

2x 2TB drives

2x 4TB drives

I'm now running into "not enough space" errors after only utilizing 2.71 TB of space on the volume. I went into Server Manager to check out the used space at the disk level and found that each disk has exactly the same amount of used space: 931GB. This is the exact total available capacity of my smallest disk in the pool. To me, this is indicative of behavior I would expect had I created a hardware RAID 0+1 array (a mirror of 3 striped disks). I was under an assumption based on the articles I've read pertaining to SS that a two-way mirror would arrange the mirrors and columns to essentially be a RAID 10 layout (a stripe of mirrored pairs of equal capacity).

Have I setup the array incorrectly? If so, is there a way to tell SS to "pair" or assign the disks that are the same capacity to each other (for the mirrors) and also have the 3 columns of alike-pairs striped?

Thanks!SS Capacity Error 02.jpg SS Capacity Error.jpg


Active Member
Aug 14, 2018
I think that this makes sense-three columns means data is striped across three disks as written. Mirror doubles that. So your smallest drives are full@931 GB, it can't write more due to the column layout. If you drop back to 2 column, mirror it should work as you expect.
(I've got a similar setup, 3x 2tb, 1 1tb, 2x 750gb, 1 250gb, but I setup without playing with columns, so I think it is just 2 column, might be single) Edit: Just checked, I'm single column.

This is a really good explainer:
Storage Spaces Stripping and Mirroring
Also see this:

A two column, two-way mirror space that uses thin provisioning in a four disk pool
Two of the disks have 1TB capacity and two have 2TB capacity. Because a two column, two-way mirror space needs four disks (number_of_disks = NumberOfColumns * NumberOfDataCopies), it will evenly consume all four disks as it writes new data. When capacity utilization of the two 1TB disks reaches 70%, Storage Spaces will warn of a low capacity condition. Even though the entire pool has 3.2TB free capacity, the thinly provisioned space will soon not be able to write any more data because the 1TB disks are nearly fully consumed.
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