I extended the /home LVM volume for my KVM guest by 500G via
lvresize -v -L +500G /dev/engi/v-sbuild-home
and rebooted my guest system to update the available disk space.
After the reboot I wanted to use resize2fs to enlarge the home partition on my Debian guest. It returned with an error that the filesystem is already 104857600 blocks big and there is nothing to do for the filesystem.
I than checked in parted and fdisk how big the disk is and it still shows the old 400GiB instead of the 900 GiB. qemu-img and virt-manager on the host show the correct enlarged disk size. Is there any way to force a rescan on the guest or did I forget anything in my workflow? I resized another home partition the exact same way a few weeks before without any problems. If you need any more information please ask.
Thanks in advance for all your help.