Q. How can I check how many disks from my storage pool are being used for a certain virtual disk in Storage Space?

A. In Windows Server 2012, Storage Spaces refers to columns as the underlying physical disks that a stripe of data is written to (a stripe being one pass of written data). Interleave represents the amount of data written to a single column per stripe; for example, by default the interleave is 256KB.

This means a virtual disk with a column value of 5 is using five physical disks from the Storage Pool; and with an interleave of 256KB, the stripe width (that single pass of data) is 256KB * 5 which equals 1280KB.

It doesn't matter if the virtual disk is using mirroring, parity, and how those columns are being used, the column value will always show the total number of disks being used. But as you use mirroring and parity, the stripe width value would include parity/mirror data, so it wouldn't reflect the actual original data being written, as those parity/mirrored data blocks are included in the stripe size.

This can be examined using several methods. Below, I use Windows PowerShell. Notice you can see the Interleave value and also the NumberOfColumns value and you can see I'm using the Parity option through the ResiliencySettingName value with detail shown in the ParityLayout value:

Get-VirtualDisk -friendlyname VirtualsDrive | fl
ObjectId : {b3f76b32-875d-11e2-9410-0015173a4249}
PassThroughClass :
PassThroughIds :
PassThroughNamespace :
PassThroughServer :
UniqueId : 326BF7B35D87E21194100015173A4249
Access : Read/Write
AllocatedSize : 953482739712
DetachedReason : None
FootprintOnPool : 1191853424640
FriendlyName : VirtualsDrive
HealthStatus : Healthy
Interleave : 262144
IsDeduplicationEnabled : False
IsEnclosureAware : False
IsManualAttach : False
IsSnapshot : False
LogicalSectorSize : 512
Name :
NameFormat :
NumberOfAvailableCopies : 0
NumberOfColumns : 5
NumberOfDataCopies : 1
OperationalStatus : OK
OtherOperationalStatusDescription :
OtherUsageDescription :
ParityLayout : Rotated Parity
PhysicalDiskRedundancy : 1
PhysicalSectorSize : 4096
ProvisioningType : Fixed
RequestNoSinglePointOfFailure : True
ResiliencySettingName : Parity
Size : 953482739712
UniqueIdFormat : Vendor Specific
UniqueIdFormatDescription :
Usage : Other
PSComputerName :