Merge pull request #737 from mwhudson/better-lvm-default

have the lv created by the guided lvm option take up 80% of the vg

subiquity/controllers/filesystem.py

@@ -750,14 +750,26 @@ class FilesystemController(SubiquityController):
         spec = dict(name="ubuntu-vg", devices=set([part]))
         if lvm_options and lvm_options['encrypt']:
             spec['password'] = lvm_options['luks_options']['password']
-        # create volume group on partition
         vg = self.create_volgroup(spec)
-        target_size = dehumanize_size("4G")
-        if target_size > vg.free_for_partitions:
-            target_size = int(vg.size*0.8)
+        # There's no point using LVM and unconditionally filling the
+        # VG with a single LV, but we should use more of a smaller
+        # disk to avoid the user running into out of space errors
+        # earlier than they probably expect to.
+        if vg.size < 10 * (2 << 30):
+            # Use all of a small (<10G) disk.
+            lv_size = vg.size
+        elif vg.size < 20 * (2 << 30):
+            # Use 10G of a smallish (<20G) disk.
+            lv_size = 10 * (2 << 30)
+        elif vg.size < 200 * (2 << 30):
+            # Use half of a larger (<200G) disk.
+            lv_size = vg.size // 2
+        else:
+            # Use at most 100G of a large disk.
+            lv_size = 100 * (2 << 30)
         self.create_logical_volume(
             vg=vg, spec=dict(
-                size=target_size,
+                size=lv_size,
                 name="ubuntu-lv",
                 fstype="ext4",
                 mount="/",

subiquity/ui/views/filesystem/guided.py

@@ -140,9 +140,10 @@ If the platform requires it, a bootloader partition is created on the disk.
 
 If you choose to use LVM, two additional partitions are then created,
 one for /boot and one covering the rest of the disk. An LVM volume
-group is created containing the large partition. A 4 gigabyte logical
-volume is created for the root filesystem. It can easily be enlarged
-with standard LVM command line tools.
+group is created containing the large partition. A logical volume is
+created for the root filesystem, sized using some simple heuristic. It
+can easily be enlarged with standard LVM command line tools (or on the
+next screen).
 
 You can also choose to encrypt LVM volume group. This will require
 setting a password, that one will need to type on every boot before