Seeing chunk extent read failures on what I believe is a MAAS installer boot:
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/var/lib/cloud/instances/rs3me7/datasource: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/var/lib/cloud/data/previous-datasource: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/var/lib/cloud/data/instance-id: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/var/lib/cloud/data/previous-instance-id: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/var/lib/cloud/instance/obj.pkl: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/var/lib/cloud/instances/rs3me7/user-data.txt: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/var/lib/cloud/instances/rs3me7/user-data.txt.i: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/var/lib/cloud/instances/rs3me7/vendor-data.txt: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/var/lib/cloud/instances/rs3me7/vendor-data.txt.i: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/var/lib/cloud/instances/rs3me7/sem/consume_data: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/var/lib/cloud/instance/scripts/user_data.sh: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/var/lib/cloud/instances/rs3me7/vendor-cloud-config.txt: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/var/lib/cloud/instances/rs3me7/sem/config_ubuntu_init_switch: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/var/lib/cloud/instances/rs3me7/sem/config_seed_random: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/var/lib/cloud/instances/rs3me7/sem/config_write_files: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/var/lib/cloud/instances/rs3me7/sem/config_set_hostname: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/etc/hostname: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/var/lib/cloud/data/previous-hostname: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/var/lib/cloud/instances/rs3me7/sem/config_ca_certs: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/var/lib/cloud/instances/rs3me7/sem/config_rsyslog: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/etc/rsyslog.d/20-cloud-config.conf: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/var/lib/cloud/instances/rs3me7/sem/config_users_groups: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/etc/gshadow: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/etc/shadow: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/home/ubuntu/.profile: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/home/ubuntu/.bash_logout: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/home/ubuntu/.bashrc: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/etc/passwd-: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/etc/shadow-: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/etc/group-: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/etc/gshadow-: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/etc/subuid-: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/etc/subgid-: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/etc/sudoers.d/90-cloud-init-users: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/var/lib/cloud/instances/rs3me7/sem/config_ssh: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/etc/ssh/ssh_host_rsa_key: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/etc/ssh/ssh_host_rsa_key.pub: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/etc/ssh/ssh_host_dsa_key: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/etc/ssh/ssh_host_dsa_key.pub: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/etc/ssh/ssh_host_ecdsa_key: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/etc/ssh/ssh_host_ecdsa_key.pub: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/etc/ssh/ssh_host_ed25519_key: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/etc/ssh/ssh_host_ed25519_key.pub: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/home/ubuntu/.ssh/authorized_keys: Error retrieving chunk extents: Operation not supported
Sep 27 23:13:57 clear-teal ureadahead[1066]: ureadahead:/root/.ssh/authorized_keys: Error retrieving chunk extents: Operation not supported
Note that this is not reporting these errors on all files accessed during boot (by a long way) so we need to understand what is special about those. I believe this is a MAAS boot and may be using bind mounts over squashfs. Need to confirm.