How can I compact the VHD file with Ubuntu?

I use windows server 2008r2 with role Hyper-V. The guest system is Ubuntu 12.04 LTC. It is situated on the dynamic virtual hard disk.

I want to compact this VHD (The real size is 50 GB, 360 GB on the disk). But I can not do this, because the Ubuntu file system is not NTFS. What do I need (gparted, sdelete, ...) for solving this problem?

The main problem is that the filesystem is not NTFS, but ext4.

The answer:

1) Download systemrescuecd

http://sourceforge.net/projects/systemrescuecd/files/sysresccd-x86/3.8.1/systemrescuecd-x86-3.8.1.iso/download

2) Add this .iso to the quest OS Ubuntu

3) Start this virtual machine

4) Use zerofree

zerofree /dev/sda1

5) Poweroff this virtual machine

6) Use Hyper-V manager (Edit -> defragmentation)

This vhd was 360 Gb. Now 70 GB.

Poweroff your VM, backup the VHD, and run another virtual machine (I use SystemRescueCD since it's small and fast) that has the ext4 partition available to it, i.e., a HD for SysRescue (but don't mount it!). From the SysRescue VM, run 'zerofree' on the ext4 partition, poweroff that VM, and then use your Administration Website to compact the VHD.

I can confirm: zerofree is working to compact virtual disk files

BUT: you don't need to use any rescue CDs or to mount the VHDX in another virtual machine:

sudo apt-get install zerofree

Boot into recovery mode, then run:

zerofree /dev/sda1

After that, we have to start the optimization for the virtual disk file. On the server hosting the VHDX file, create the following file ShrinkVhdx.ps1:

[CmdletBinding()]
Param(
    $VHDFiles
)

# Find the disks
foreach($VHD in $VHDFiles){
    Write-Verbose "Working on $VHD, please wait"
    Write-Verbose "Current size $([math]::truncate($(Get-VHD -Path $VHD).FileSize/ 1GB)) GB"
    
    Mount-VHD -Path $VHD -NoDriveLetter -ReadOnly
    Optimize-VHD -Path $VHD -Mode Full

    Write-Verbose "Optimize size $([math]::truncate($(Get-VHD -Path $VHD).FileSize/ 1GB)) GB"
    Dismount-VHD -Path $VHD
    
    Write-Verbose ""
}

And now run the file and enjoy the released disk space :-)

ShrinkVhdx.ps1 .\hdd1.vhdx

The process appears to be

Backup your current VHD file.
Use Snapshot manager to delete/merge any snapshots.
Zero fill the unused disk space

viz

sudo apt-get install secure-delete 
sudo sfill -llz .

This creates a file called oooooooo.ooo filled with 0s. You should repeat the sfill command on all partitions I guess.

Note this isn't quick either, it will take hours if not days to complete.

Compact
Profit