lvm: added guide to extend volumes

wiki/linux/lvm.md

@@ -12,3 +12,36 @@ partition table and will display the error `Device /dev/sdb excluded by a filter
 This can be solved by removing the old partition table with `wipefs -a /dev/sdb`.
 And finally create the volume group `vgcreate vmdata /dev/sdb`.
 Then follow the guide in proxmox on how to connect a `vg` to proxmox.
+
+## Add Drive to existing volume group
+
+First format the disk so that it has one partition (we will assume its called
+`/dev/sdc1`).
+To add the partition to a group run:
+
+```shell
+pvcreate /dev/sdc1
+vgextend <name of your volume group> /dev/sdc1
+```
+
+## Increase size of a logical volume
+
+To increase the size of the logical volume you need to have free space in the
+according volume group. You can check that by running: `vgdisplay`.
+Then run:
+
+```shell
+lvextend -L +<size (e.g. 40G)> /dev/<volume groupt>/<logical volume>
+```
+
+If you want to allocate all the free space existing in a volume group run:
+
+```shell
+lvextend -l +100%FREE /dev/<volume group>/<logical volume>
+```
+
+Now you need to extend the filesystem with:
+
+```shell
+resize2fs /dev/<volume group>/<logical volume>
+```