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Disk2VHD image backup with automatic removal of old images when backup drive is full

I've got the following script that I'm running as scheduled task each day.

It makes a VHD image of C: drive (447 GB) and copy it to F: drive (3,63 TB) and removes old vhd images when there is more than 4 of these.

I would like to modify it so it would take current disk space usage from C drive and compare it with current disk usage of F drive. If there will be less space on F than it's needed to backup whole C then the last image would be removed.

It would be good to use fsutil utility:

C:\Users\Marek>fsutil volume diskfree c:
Całkowita liczba bajtów wolnych : 244490219520
Całkowita liczba bajtów : 480127946752
Całkowita liczba dostępnych bajtów wolnych: 244490219520

C:\Users\Marek>fsutil volume diskfree f:
Całkowita liczba bajtów wolnych : 324223422464
Całkowita liczba bajtów : 4000575385600
Całkowita liczba dostępnych bajtów wolnych: 324223422464

REM
REM A simple backup system using disk2vhd
REM
REM version 1.3, by J.E.B., 2011-02-22
REM
REM requires 'disk2vhd.exe' to be in the path
REM

setLocal EnableDelayedExpansion

REM "DRIVES" can be one drive identifier with colon, multiple separated by spaces,
REM or asterisk for all.
REM "DEST" can be a drive letter or a UNC.

SET DRIVES="C:"
SET DEST="F:"

REM Keep most recent 4 VHD files in DEST, delete the rest

for /f "skip=4 tokens=* delims= " %%a in ('dir/b/o-d %DEST%\*.VHD') do (
del %DEST%\%%a
)

REM Backup to VHD

C:
cd \
DISK2VHD %DRIVES% %DEST%\%COMPUTERNAME%--%date:~-10,3%%date:~-7,2%%date:~-4,4%.VHD

EXIT /B n

Tony J

I've just knocked up the following powershell script but can't easily test it's individual components.

It's possibly not the most graceful solution, if I'm honest, but it should work.

I put the /1073741824 in whilst I was testing as it made for easier numbers on the eye. There's no functional reason for it to remain unless you wanted to pipe some of the variables out.

#This function is called repeatedly until the space on the F: drive is greater than the used space on the C: drive
function DiskSpace() {
$Cdisk = Get-WmiObject Win32_LogicalDisk -Filter "DeviceID='C:'" | Select-Object Size,FreeSpace
$Fdisk = Get-WmiObject Win32_LogicalDisk -Filter "DeviceID='F:'" | Select-Object Size,FreeSpace
$CdiskCapacity = $Cdisk.size/1073741824
$CdiskFree = $Cdisk.freespace/1073741824
$CdiskUSed = $CdiskCapacity-$CDiskFree
$fdisk = $fdisk.freespace/1073741824

return $Fdisk, $cdiskUsed
}

#This function will simply delete the oldest file in the root of the F: drive
Function DelVHD {
Get-ChildItem F:\ | Sort CreationTime | Select -First 1 | Remove-Item -force
}

#Once enough free space has been created on F: this function creates the latest VHD
Function CreateVHD {
$filename = (get-date -uformat %d%b%y) + "_"  + $Env:COMPUTERNAME + ".vhd"
.\disk2vhd c: ("F:\" +$filename) # The .\ assumes disk2vhd is in the same folder as this script;
}

#This loop kicks everything off - it gets the free disk space, deletes files one at a time on F: as required and then creates the VHD when there is sufficient disk space freed up.
Do {
if ($fdisk -lt $Cdiskused) {
write-host "Not enough free space on F: Drive. Deleting oldest image"
DelVHD
diskspace
}
}
until ($fdisk -gt $Cdiskused)

write-host "Enough free space on F:\ found...creating latest VHD"
CreateVHD