Compare-Object returning unexpected output - powershell

Question

I have created a small function that captures Get-Volume into a local file. The next time the function runs, it compares the output of a fresh Get-Volume with the one previously saved to the file system.
This function works perfectly for services but is strangely returning a volume as 'different' even though we can see from the output it is not.
function Compare-Volumes{
$Path = "$Env:PROGRAMDATA\VACS\states\"
$File = "volumes.csv"
$Volumes = Get-Volume | Select-Object OperationalStatus, HealthStatus, DriveType, FileSystemType, DedupMode, UniqueId, AllocationUnitSize, DriveLetter, FileSystem, FileSystemLabel, Size
if (![System.IO.File]::Exists($Path+$File)){
$Volumes | Export-CSV -Path $Path$File -Force
}else{
# Load file to object, get differences, submit to API, replace previous snapshot in file with new one
$Snapshot = Import-CSV -Path "$Path$File"
$StatusChanges = Compare-Object -ReferenceObject ($Snapshot) -DifferenceObject ($Volumes) -Property OperationalStatus, HealthStatus, DriveType, FileSystemType, DedupMode, UniqueId, AllocationUnitSize, DriveLetter, FileSystem, FileSystemLabel, Size -IncludeEqual
$StatusChanges
$Volumes | Export-CSV -Path $Path$File -Force
}
}
My expected results are that everything returns as equal/unchanged (==) as none of the properties change, as is clear in the output below. Yet for some reason, the SideIndicator property added by Compare-Object is indicating value differences for the volume labelled Recovery.
OperationalStatus : Unknown
HealthStatus : Healthy
DriveType : CD-ROM
FileSystemType : Unknown
DedupMode : Disabled
UniqueId : \\?\Volume{2b4803c9-1ebe-11e6-9bed-005056c00008}\
AllocationUnitSize : 0
DriveLetter : E
FileSystem :
FileSystemLabel :
Size : 0
SideIndicator : ==
OperationalStatus : OK
HealthStatus : Healthy
DriveType : Fixed
FileSystemType : NTFS
DedupMode : NotAvailable
UniqueId : \\?\Volume{f688d14f-0ee7-11e5-b210-806e6f6e6963}\
AllocationUnitSize : 4096
DriveLetter : C
FileSystem : NTFS
FileSystemLabel : Windows
Size : 953903214592
SideIndicator : ==
OperationalStatus : Unknown
HealthStatus : Healthy
DriveType : CD-ROM
FileSystemType : Unknown
DedupMode : Disabled
UniqueId : \\?\Volume{f688d152-0ee7-11e5-b210-806e6f6e6963}\
AllocationUnitSize : 0
DriveLetter : D
FileSystem :
FileSystemLabel :
Size : 0
SideIndicator : ==
OperationalStatus : OK
HealthStatus : Healthy
DriveType : Fixed
FileSystemType : NTFS
DedupMode : NotAvailable
UniqueId : \\?\Volume{f688d14e-0ee7-11e5-b210-806e6f6e6963}\
AllocationUnitSize : 4096
DriveLetter :
FileSystem : NTFS
FileSystemLabel : Recovery
Size : 6291451904
SideIndicator : =>
OperationalStatus : OK
HealthStatus : Healthy
DriveType : Fixed
FileSystemType : NTFS
DedupMode : NotAvailable
UniqueId : \\?\Volume{f688d14e-0ee7-11e5-b210-806e6f6e6963}\
AllocationUnitSize : 4096
DriveLetter :
FileSystem : NTFS
FileSystemLabel : Recovery
Size : 6291451904
SideIndicator : <=

Answer 1

Strangely it is the DriveLetter property which compares falsely
with volumes which doesn't have one (like the recovery partition).
Presumably you'll have to include a Select-Object with a calculated property
which also checks the DriveLetter [string]::IsNullOrEmpty()
to avoid comparing $Null with the stringified output "" of Export-Csv
Your script, a bit streamlined:
## Q:\Test\2018\12\31\SO_53990220.ps1
function Compare-Volumes{
$FilePath = Join-Path "$Env:PROGRAMDATA\VACS\states\" "volumes.csv"
$Volumes = Get-Volume | Select-Object OperationalStatus,HealthStatus,DriveType,
FileSystemType, DedupMode,UniqueId,AllocationUnitSize,FileSystemLabel,FileSystem,Size,
#{n='DriveLetter';e={if([string]::IsNullOrEmpty($_.DriveLetter)){""}else{$_.DriveLetter}}}
if (Test-Path $FilePath){
# Load file to object, get differences, submit to API, replace previous snapshot in file with new one
$Snapshot = Import-CSV -Path $FilePath
$StatusChanges = Compare-Object -ReferenceObject ($Snapshot) -DifferenceObject ($Volumes) `
-IncludeEqual -Property OperationalStatus,HealthStatus,DriveType,FileSystemType,
DedupMode,UniqueId,AllocationUnitSize,FileSystemLabel,FileSystem,Size,
DriveLetter
$StatusChanges
}
$Volumes | Export-CSV -Path $FilePath -Force -NoTypeInformation
}
Compare-Volumes