Comment 6 for bug 1634678

$ dpkg-query --show cloud-init
cloud-init 0.7.9-90-g61eb03fe-0ubuntu1~16.10.1

$ grep /mnt /proc/mounts
/dev/vdb1 /mnt ext4 rw,relatime,data=ordered 0 0

$ sudo blkid /dev/vdb1
/dev/vdb1: LABEL="mydata" UUID="20a0d834-2aca-450c-8d4d-a9e0a3fa74da" TYPE="ext4" PARTUUID="4d3c51ff-449e-4497-9ddc-54143b531095"

$ echo $(date -R) hi mom | sudo tee -a /mnt/my-important-data.txt
Mon, 17 Apr 2017 14:21:07 +0000 hi mom

$ sudo rm -Rf /var/lib/cloud /var/log/cloud-init*
$ sudo reboot

...
# ssh back in

$ grep cc_disk_setup.py /var/log/cloud-init.log
2017-04-17 14:22:05,078 - stages.py[DEBUG]: Running module disk_setup (<module 'cloudinit.config.cc_disk_setup' from '/usr/lib/python3/dist-packages/cloudinit/config/cc_disk_setup.py'>) with frequency once-per-instance
2017-04-17 14:22:05,080 - cc_disk_setup.py[DEBUG]: setting up filesystems: [{'label': 'mydata', 'partition': 'auto', 'device': '/dev/vdb', 'filesystem': 'ext4'}]
2017-04-17 14:22:05,166 - cc_disk_setup.py[DEBUG]: Creating new filesystem.
2017-04-17 14:22:05,166 - cc_disk_setup.py[DEBUG]: Checking /dev/vdb against default devices
2017-04-17 14:22:05,166 - cc_disk_setup.py[DEBUG]: Identifying device to create mydata filesytem on
2017-04-17 14:22:05,176 - cc_disk_setup.py[DEBUG]: Automatic device for /dev/vdb identified as /dev/vdb1
2017-04-17 14:22:05,176 - cc_disk_setup.py[DEBUG]: Found filesystem match, skipping formating.

$ cat /mnt/my-important-data.txt
Mon, 17 Apr 2017 14:21:07 +0000 hi mom