Shrinking volumes under Qubes 4.0
=================================

The [official documentation](https://www.qubes-os.org/doc/resize-disk-image/#shrinking-a-disk-image) describes a safe(ish) way of "shrinking" a VM's volume. This is the recommended approach of shrinking an AppVM's private volume, but it has two caveats:

- it requires copying data, which can take a while
- it is limited to the private volume of VMs based on TemplateVMs

This document describes how to shrink *any* volume.

**The instructions given below are error-prone. ALWAYS BACKUP your data before attempting to shrink a volume.**.

Note: Qubes 4.0 uses *thin* LVM storage: only the data present on a volume uses disk space, free space isn't allocated physically. If your only concern is disk space, you may simply be careful with how much data you store in a given volume and avoid having to shrink a volume (use `sudo lvs` in dom0 and compare the `LSize` vs `Data%` fields to find out about real disk usage).

The procedure for shrinking a volume on Ext4 and most other filesystems is a bit convoluted because they don't support online shrinking, and we don't want to process any untrusted data in dom0.

The instructions below show how to resize a VM's private volume. For root volumes, swap the `-private` volume suffix with `-root`.

1. backup your data with `qvm-clone` , `qvm-backup`, or your own backup mechanism. Do not rely only on snapshots (yet)
2. stop the VM (eg. 'largeVM') whose volume has to be resized
3. start another VM (eg. 'tempVM') with largeVM's private volume attached:

    ~~~
    qvm-start --hddisk dom0:/dev/qubes_dom0/vm-largeVM-private tempVM
    ~~~

    Alternatively, you could setup a loop device in dom0 associated to largeVM's private volume and attach it to a running VM but this is outside the scope of this document (see `losetup` and `qvm-block`).

4. in tempVM, resize the attached volume (for instance to 2 GB):

    ~~~
    sudo e2fsck -f /dev/xvdi
    sudo resize2fs /dev/xvdi 2G
    ~~~

5. shutdown tempVM

6. in dom0, resize the lvm volume to the **SAME** size you used at step 4. (specifying a lower size than the underlying filesystem's size would corrupt the filesystem and either destroy some of your data or trigger filesystem exceptions when the filesystem tries to write at a location that doesn't exist):

    ~~~
    sudo lvresize -L2G /dev/qubes_dom0/vm-largeVM-private
    ~~~

The procedure is the same for other OSes (eg. MS Windows) but you'll have to use OS specific tools to resize the volume at step 4. and to be careful to specify the right shrinked size at step 6.