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I'm trying to understand how "smart" Windows Storages Spaces is when it comes to using disks with different capacities.

Example:

  1. I create a Storage Pool using a 6TB physical disk and a 10TB physical disk .
  2. Then I create a 6TB Mirrored Storage Space and fill it to capacity with data.
  3. I create a 4TB Simple Storage Space on that same Storage Pool.

Will I:

  • Be able to store 4TB of data on that Simple Storage Space (which in turn must be storing the data physically on the 10TB disk), or
  • Be unable to store anything on the 4TB

If it isn't smart enough to automatically use all the space on the 10TB disk, is there special setting or PowerShell way to force it to put the Simple Storage Space on the 10TB disk?

Thanks!

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2 Answers 2

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A Space isn't a RAID volume and isn't placed on any single disk in particular. Storage Spaces stores data in 256 MB "slabs", placing them on whichever disks have space available. (If you created a "mirrored" Space volume across five disks, there would still be only two copies of each slab, placed on any two disks available – the volume would not be duplicated across all five disks, nor would it be limited to designated pairs of mirrored disks.)

So if the pool has a disk with 4TB of space available, and if one disk is enough to satisfy the redundancy requirements of that particular volume, Storage Spaces will most likely just keep placing new slabs on that disk until it fills up completely.

(It will be less than 4TB though as some space is needed to track Spaces metadata, i.e. mapping of logical sectors to physical slab location.)

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I confirmed that Storages Spaces is not smart enough handle different-sized disks. (using Windows 11 as of 10/12/2022)

Specifically, I had a 6TB and a 12TB physical disks. I created a 6TB two-way mirror and filled it with data. Then I create a 6TB simple (no redundancy) stoarage space and tried to fill it with data. But I got an out of space error.

So, basically, Windows Storage Spaces is preventing me from using 6TBs of the space on my larger physical drive.

Here's the evidence:

Screenshot of Manage Storage Spaces tool

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  • On your screenshot, you have 11.9TB + 5.45TB physical disks, but you try to create 6TB simple + 6TB mirrored. 11.9+5.45 < 18 , so this screenshot looks like there's simply not enough raw capacity for what your want.
    – i3v
    Commented Oct 19, 2022 at 23:16
  • The storage spaces are thin provisioned. en.m.wikipedia.org/wiki/Thin_provisioning
    – SSG
    Commented Oct 21, 2022 at 0:08
  • My idea was that overprovisioning might cause that warning, like in some other systems. But that seem to be not the case for SS. Also, there's ThinProvisioningAlertThresholds parameter (70 by default), but in your case, (1.16+9.74)/(11.9+5.45)=0.63, so it should not produce any warning either... Anyway, the out of space error is the evidence, the warning is just a warning. Btw, have you tried the Optimize usage?
    – i3v
    Commented Oct 21, 2022 at 17:41

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