#XFS doesn't support shrinking - i did it anyway, on the boot mirror of my #Ubuntu server.
1st: backup
2nd: backup again using xfsdump
3rd: unmount, nuke md-mirror, create new md-mirror, and mkfs.xfs
4th: mount and xfsrestore
5th: fix fstab, take a photo of blkid and reboot
6th: learn how to use the grub shell and boot into Ubuntu
7th: dpkg-reconfigure grub-efi-amd64 in order to fix grub, then update-initramfs -ukall
8th: reboot again to make sure it's actually fixed
Q'Pla!
…now, why did i commit such heresy?
My VMs boot from spinning HDDs - slow!
I'll create a new ZFS mirror with the now free SSD capacity, and migrate the VM boot volumes over to the faster and more responsive storage backend.
Those VMs will have a data partition on spinning rust. I only want the OS on faster storage.
That should speed up patch days and reboots.