Richard Siddaway's Blog

I have heard some discussions recently regarding whether Win32_LogicalDisk or Win32_Volume should be used in the answer to event 3 in the Scripting Games.

The problem requires you pull the drive letter, drive size and freespace for local disks on the server. Notice the emphasis – that will be important.

Looking at Win32_Volume

PS> Get-CimClass -ClassName Win32_Volume | select -ExpandProperty CimClassproperties  | select Name

Name
----
Caption
Description
InstallDate
Name
Status
Availability
ConfigManagerErrorCode
ConfigManagerUserConfig
CreationClassName
DeviceID
ErrorCleared
ErrorDescription
LastErrorCode
PNPDeviceID
PowerManagementCapabilities
PowerManagementSupported
StatusInfo
SystemCreationClassName
SystemName
Access
BlockSize
ErrorMethodology
NumberOfBlocks
Purpose
Automount
BootVolume
Capacity
Compressed
DirtyBitSet
DriveLetter
DriveType
FileSystem
FreeSpace
IndexingEnabled
Label
MaximumFileNameLength
PageFilePresent
QuotasEnabled
QuotasIncomplete
QuotasRebuilding
SerialNumber
SupportsDiskQuotas
SupportsFileBasedCompression
SystemVolume

You see 3 properties that might be of use

Get-CimInstance -ClassName Win32_Volume | select DriveLetter, Capacity, FreeSpace

is a start but I get two drives with no capacity & freespace – must by my DVD drives

I can filter those out using drive type.  DriveType =3 gives me local disks

So the WMI call I need is

Get-CimInstance -ClassName Win32_Volume -Filter "DriveType=3"  | select DriveLetter, Capacity, FreeSpace

Get-WmiObject -Class Win32_Volume -Filter "DriveType=3"  | select DriveLetter, Capacity, FreeSpace

Now lets look at Win32_LogicalDisk

PS> Get-CimClass -ClassName Win32_Logicaldisk | select -ExpandProperty CimClassproperties  | select Name

Name
----
Caption
Description
InstallDate
Name
Status
Availability
ConfigManagerErrorCode
ConfigManagerUserConfig
CreationClassName
DeviceID
ErrorCleared
ErrorDescription
LastErrorCode
PNPDeviceID
PowerManagementCapabilities
PowerManagementSupported
StatusInfo
SystemCreationClassName
SystemName
Access
BlockSize
ErrorMethodology
NumberOfBlocks
Purpose
FreeSpace
Size
Compressed
DriveType
FileSystem
MaximumComponentLength
MediaType
ProviderName
QuotasDisabled
QuotasIncomplete
QuotasRebuilding
SupportsDiskQuotas
SupportsFileBasedCompression
VolumeDirty
VolumeName
VolumeSerialNumber

I can’t find a DriveLetter but I know that DeviceId supplies that information – if in doubt check by displaying all properties of one instance or do this

PS> Get-CimInstance -ClassName Win32_Logicaldisk | ft -a

DeviceID DriveType ProviderName VolumeName      Size         FreeSpace
-------- --------- ------------ ----------      ----         ---------
C:       3                                      249951154176 146292559872
D:       3                      System Reserved 104853504    69279744
E:       2
F:       5

Drivetype matches with Win32_Volume so we get

Get-CimInstance -ClassName Win32_Logicaldisk | Select Deviceid, Size, FreeSpace
Get-WmiObject -Class Win32_Logicaldisk | Select Deviceid, Size, FreeSpace

You’ll have noticed that D: has a volume name of System Reserved. This means its a system disk that you shouldn’t be touching. Technically the event asked for information on local disks so it should be included. I know that some purists will argue against this so to remove the system volume you can

PS>  Get-CimInstance -ClassName Win32_Volume -Filter "DriveType=3 AND SystemVolume = $false"  | select DriveLetter, Capacity, FreeSpace

or

PS> Get-CimInstance -ClassName Win32_Logicaldisk -Filter "DriveType = 3 AND VolumeName <> 'System Reserved'" | select DeviceId, Size, FreeSpace

So either will give you the results you need.  You just need to dig into the classes a bit.

In event 3 you have to get information on hard disk capacity.  I’ve only looked at the first couple of dozen scripts but seen this too many times

Get-WmiObject -Class Win32_LogicalDisk | where DriveType -eq 3

or if you prefer the version 2 way

Get-WmiObject -Class Win32_LogicalDisk | where {$_.DriveType -eq 3}

If puppies get terminated for using Write-Host this sort of construct should triggers a mass extinction.

When pulling information back with WMI (or any other technique) from a remote server ALWAYS, ALWAYS, ALWAYS filter on the remote server.  What you are doing here is pulling back all of the data and filtering on the client. This is grossly inefficient when you are dealing with hundreds of machines.

The PowerShell team gave us the –Filter parameter on Get-WmiObject for a reason. Its to do the filtering on the remote server.

Get-WmiObject -Class Win32_LogicalDisk -Filter "DriveType = 3"

If you are guilty of not using –Filter write out 100 times “I must filter on the remote server”

And no – you can’t write a PowerShell script to do it for you!