diff --git a/aegea/launch.py b/aegea/launch.py
index 7e3f3cea..917f9b17 100644
--- a/aegea/launch.py
+++ b/aegea/launch.py
@@ -135,7 +135,7 @@ def launch(args):
                        KeyName=ssh_key_name,
                        SecurityGroupIds=[sg.id for sg in security_groups],
                        InstanceType=args.instance_type,
-                       BlockDeviceMappings=get_bdm(ebs_storage=args.storage),
+                       BlockDeviceMappings=get_bdm(ami=args.ami, ebs_storage=args.storage),
                        UserData=get_user_data(**user_data_args))
     tag_spec = dict(ResourceType="instance", Tags=encode_tags(instance_tags))
     logger.info("Launch spec user data is %i bytes long", len(launch_spec["UserData"]))
@@ -220,6 +220,11 @@ def instance_types(self, **kwargs):
 
 parser = register_parser(launch)
 parser.add_argument("hostname")
+parser.add_argument("--storage", nargs="+", metavar="MOUNTPOINT=SIZE_GB",
+                    type=lambda x: x.rstrip("GBgb").split("=", 1),
+                    help="At launch time, attach EBS volume(s) of this size, format and mount them.")
+parser.add_argument("--efs-home", action="store_true",
+                    help="Create and manage an EFS filesystem that the instance will use for user home directories")
 parser.add_argument("--commands", nargs="+", metavar="COMMAND", help="Commands to run on host upon startup")
 parser.add_argument("--packages", nargs="+", metavar="PACKAGE", help="APT packages to install on host upon startup")
 parser.add_argument("--ssh-key-name")
@@ -248,11 +253,6 @@ def instance_types(self, **kwargs):
                     help="Tags to apply to launched instances.")
 parser.add_argument("--wait-for-ssh", action="store_true",
                     help="Wait for launched instance to begin accepting SSH connections. Security groups and NACLs must permit SSH from launching host.")  # noqa
-parser.add_argument("--efs-home", action="store_true",
-                    help="Create and manage an EFS filesystem that the instance will use for user home directories")
-parser.add_argument("--storage", nargs="+", metavar="MOUNTPOINT=SIZE_GB",
-                    type=lambda x: x.rstrip("GBgb").split("=", 1),
-                    help="At launch time, attach EBS volume(s) of this size, format and mount them.")
 parser.add_argument("--iam-role", default=__name__,
                     help="Pass this IAM role to the launched instance through an instance profile. Role credentials will become available in the instance metadata.")  # noqa
 parser.add_argument("--iam-policies", nargs="+", metavar="IAM_POLICY_NAME",
diff --git a/aegea/rootfs.skel/etc/cloud/cloud.cfg.d/99_aegea.cfg b/aegea/rootfs.skel/etc/cloud/cloud.cfg.d/99_aegea.cfg
index e20de43f..06c9868e 100644
--- a/aegea/rootfs.skel/etc/cloud/cloud.cfg.d/99_aegea.cfg
+++ b/aegea/rootfs.skel/etc/cloud/cloud.cfg.d/99_aegea.cfg
@@ -3,6 +3,8 @@ datasource_list: [Ec2]
 cloud_init_modules:
  - bootcmd
  - write-files
+ - growpart
+ - resizefs
  - disk_setup
  - mounts
  - set_hostname
diff --git a/aegea/util/aws/__init__.py b/aegea/util/aws/__init__.py
index 75dae046..da94631b 100644
--- a/aegea/util/aws/__init__.py
+++ b/aegea/util/aws/__init__.py
@@ -268,13 +268,21 @@ def resolve_instance_id(name):
     except IndexError:
         raise AegeaException('Could not resolve "{}" to a known instance'.format(name))
 
-def get_bdm(max_devices=12, ebs_storage=frozenset()):
+def get_bdm(ami=None, max_devices=12, ebs_storage=frozenset()):
     # Note: d2.8xl and hs1.8xl have 24 devices
     bdm = [dict(VirtualName="ephemeral" + str(i), DeviceName="xvd" + chr(ord("b") + i)) for i in range(max_devices)]
     ebs_bdm = []  # type: List[Dict]
     for i, (mountpoint, size_gb) in enumerate(ebs_storage):
-        ebs_spec = dict(Encrypted=True, DeleteOnTermination=True, VolumeType="st1", VolumeSize=int(size_gb))
-        ebs_bdm.insert(0, dict(DeviceName="xvd" + chr(ord("z") - i), Ebs=ebs_spec))
+        if mountpoint == "/":
+            rootfs_bdm = resources.ec2.Image(ami).block_device_mappings[0]
+            if "Ebs" not in rootfs_bdm or "SnapshotId" not in rootfs_bdm.get("Ebs", []):
+                raise AegeaException("Unable to locate block device mapping for root volume of {}".format(ami))
+            rootfs_bdm["Ebs"]["VolumeSize"] = int(size_gb)
+            bdm.insert(0, rootfs_bdm)
+        else:
+            volume_type = "st1" if int(size_gb) > 125 else "gp3"
+            ebs_spec = dict(Encrypted=True, DeleteOnTermination=True, VolumeType=volume_type, VolumeSize=int(size_gb))
+            ebs_bdm.insert(0, dict(DeviceName="xvd" + chr(ord("z") - i), Ebs=ebs_spec))
     bdm.extend(ebs_bdm)
     return bdm