If you dig into the classes available on a Windows machine you’ll see a mixture of prefixes – namely CIM_ and Win32_ used for the classes. So which should you use CIM_ or Win32_
Lets start by seeing whats available:
PS> Get-CimClass -ClassName *Volume* NameSpace: ROOT/CIMV2 CimClassName ------------ Win32_VolumeChangeEvent Win32_VolumeQuota Win32_VolumeQuotaSetting Win32_VolumeUserQuota CIM_StorageVolume Win32_Volume CIM_VolumeSet Win32_ShadowVolumeSupport CIM_LogicalDiskBasedOnVolumeSet Win32_ShadowDiffVolumeSupport
The CIM_ classes follow the standard definition from the DMTF – https://www.dmtf.org/standards/cim
The Win32_ classes are Microsoft’s versions of the equivalent CIM_ class often with additional properties and methods.
I’ve always recommended using the Win32_ classes because they are “optimised” for Windows. The one exception that I’ve found is CIM_Datafile that doesn’t have a Win32_ equivalent.
A question on the forum asked why this was failing
PS> Get-CimInstance -ClassName CIM_StorageVolume -Filter "DriveLetter='C:'" Get-CimInstance : Invalid query At line:1 char:1 + Get-CimInstance -ClassName CIM_StorageVolume -Filter "DriveLetter='C: ... + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + CategoryInfo : InvalidArgument: (:) [Get-CimInstance], CimException + FullyQualifiedErrorId : HRESULT 0x80041017,Microsoft.Management.Infrastructure.CimCmdlets.GetCimInstanceCommand
When this worked
PS> Get-CimInstance -ClassName CIM_StorageVolume | select Name, DriveLetter, Capacity
Name DriveLetter Capacity
---- ----------- --------
\\?\Volume{c1c4c5bb-0000-0000-0000-100000000000}\ 366997504
C:\ C: 511210610688
\\?\Volume{c1c4c5bb-0000-0000-0000-801c77000000}\ 529526784
D:\ D:
The reason is that you’re not getting back CIM_StorageVolume:
PS> Get-CimInstance -ClassName CIM_StorageVolume | Get-Member TypeName: Microsoft.Management.Infrastructure.CimInstance#root/cimv2/Win32_Volume
You’re getting Win32_Volume which DOES have a DriveLetter property. Get-WmiObject works in the same way. Looking at the properties:
PS> (Get-CimClass -ClassName CIM_StorageVolume ).CimClassProperties | Where Name -like "D*"
Name : Description
Value :
CimType : String
Flags : Property, ReadOnly, NullValue
Qualifiers : {read}
ReferenceClassName :
Name : DeviceID
Value :
CimType : String
Flags : Property, ReadOnly, NullValue
Qualifiers : {CIM_Key, read}
ReferenceClassName :
No DriveLetter. Now try Win32_Volume
PS> (Get-CimClass -ClassName Win32_Volume ).CimClassProperties | Where Name -like "D*"
Name : Description
Value :
CimType : String
Flags : Property, ReadOnly, NullValue
Qualifiers : {read}
ReferenceClassName :
Name : DeviceID
Value :
CimType : String
Flags : Property, Key, ReadOnly, NullValue
Qualifiers : {CIM_Key, read, key, MappingStrings...}
ReferenceClassName :
Name : DirtyBitSet
Value :
CimType : Boolean
Flags : Property, ReadOnly, NullValue
Qualifiers : {read}
ReferenceClassName :
Name : DriveLetter
Value :
CimType : String
Flags : Property, NullValue
Qualifiers : {read, write}
ReferenceClassName :
Name : DriveType
Value :
CimType : UInt32
Flags : Property, ReadOnly, NullValue
Qualifiers : {MappingStrings, read}
ReferenceClassName :
Win32_Volume has 2 extra properties that start with the letter D, including DriveLetter. Win32_Volume is derived from, and builds on, CIM_StorageVolume
PS> Get-WmiObject -Class Win32_Volume | select -First 1 | select -ExpandProperty __Derivation CIM_StorageVolume CIM_StorageExtent CIM_LogicalDevice CIM_LogicalElement CIM_ManagedSystemElement
If you want to get volume information on a Windows box use Win32_Volume or better still on Windows 8 and later use Get-Volume.
The only possible reason for using CIM_StorageVolume is that you’re learning more about CIM or you’re trying some cross-platform task. As I can’t think of a platform other than Windows that has implemented CIM_StorageVolume not sure how far you’ll get on the latter. If you do try CIM_StorageVolume you can filter using the Name property:
Get-CimInstance -ClassName CIM_StorageVolume -Filter "Name='C:\\'"
Note that you have to use C:\\ not C:\ because \ is an escape character in WQL.
Alternatively, use where-object to filter:
Get-CimInstance -ClassName CIM_StorageVolume | where DriveLetter -eq 'C:'
If you’re working remotely the first option is best as it reduces the amount of data being returned across the network.
If in doubt use the Win32_ class rather than the CIM class.