Unable to reclaim space in vbox disk

I am using virtual box in Ubuntu 21.04 to create VMs and test. I have one virtual machine which was using approx 70 GB data. this data was used from additional disk. as below:

puneet@puneet-PowerEdge-T30:/mnt/VMs/vms/mx19-102$ pwd
/mnt/VMs/vms/mx19-102
puneet@puneet-PowerEdge-T30:/mnt/VMs/vms/mx19-102$ du -sh *
772K    Logs
69G     mx19-102_1.vdi
8.0K    mx19-102.vbox
8.0K    mx19-102.vbox-prev
9.9G    mx19-102.vdi
808K    Snapshots
puneet@puneet-PowerEdge-T30:/mnt/VMs/vms/mx19-102$

max space is taken by mx19-102_1.vdi in host system while in actual it is not in use.

puneet@mx:~
$ lsblk
NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda      8:0    0    30G  0 disk
├─sda1   8:1    0    28G  0 part /
└─sda2   8:2    0     2G  0 part [SWAP]
sdb      8:16   0 168.8G  0 disk
└─sdb1   8:17   0 168.8G  0 part /media/data
sr0     11:0    1  1024M  0 rom
puneet@mx:~
$ df -h
Filesystem      Size  Used Avail Use% Mounted on
udev            964M     0  964M   0% /dev
tmpfs           200M  2.3M  198M   2% /run
/dev/sda1        28G  7.7G   19G  30% /
tmpfs           5.0M  4.0K  5.0M   1% /run/lock
tmpfs           809M   76K  809M   1% /dev/shm
/dev/sdb1       169G   17M  167G   1% /media/data
cgroup           12K     0   12K   0% /sys/fs/cgroup
tmpfs           200M  4.0K  200M   1% /run/user/118
tmpfs           200M     0  200M   0% /run/user/1000
puneet@mx:~
$

Disk Information:

Parent UUID:    base
State:          locked read
Type:           normal (base)
Location:       /mnt/VMs/vms/mx19-102/mx19-102_1.vdi
Storage format: VDI
Format variant: dynamic default
Capacity:       172785 MBytes
Size on disk:   70236 MBytes

Is there any way by which I can reclaim space in host system.

Shrinking a .vdi is pretty straightforward, but will require that you intentionally “fill the device to capacity”. The basic process works like this:

1. Uninstall any applications and delete any files you may not need anymore
2. Create a giant file consisting of only zeroes on the storage device you want to shrink
3. Let the file fill the entire device (this will not actually consume all the data on the host system)
4. Delete the file
5. Shut down the VM
6. Shrink the .vdi files

This sounds like a lot of work but, after one or two run-throughs, you’ll see there’s a semi-easy way to automate this down to two steps if you’re so inclined.

So let’s get started doing it “the long way”:

1. On the VM, open a Terminal (or SSH in)
2. Assuming you’ve already removed everything you don’t need, create a big file of zeroes:

   sudo dd if=/dev/zero of=/bigzero bs=4096k
   

3. Let the machine run out of space on that storage device, which will result in dd reporting an error
4. Delete the file

   sudo rm -f /bigzero
   

5. Shut down the VM

Now, on the host, do this:

1. Open a Terminal (if one is not already open)
2. Navigate to the directory with the .vdi:

   cd /mnt/VMs/vms/mx19-102
   

   ^{Note: You don’t need to be in the same directory, but it does make it easier to verify the shrunken file size after the upcoming operation.}
3. Shrink the .vdi:

   VBoxManage modifymedium disk mx19-102_1.vdi --compact 
   

   You will see the progress as the tool outputs it’s completion status like this:

   0%...10%...20%...30%...40%...50%...60%...70%...80%...90%...100%
   

4. Verify the results:

   du -sh *
   772K    Logs
   30G     mx19-102_1.vdi
   8.0K    mx19-102.vbox
   8.0K    mx19-102.vbox-prev
   9.9G    mx19-102.vdi
   808K    Snapshots
   

There are quite a few useful operations that modifymedium enables if you ever need to change an attribute of the virtual storage device.