Persistent Storage

Raw compute power without persistent storage only supports a limited range of applications. StratusLab like most cloud software also provides services for managing persistent storage.

For StratusLab, persistent storage is in the form of raw block devices (volumes). These volumes can be used in conjunction with virtual machines, but importantly have a lifecycle that is independent of them.

Raw block devices behave similarly to physical hard drives. In particular, they have some of the same limitations:

  • They are initially empty and unformatted; they must be initialized when first used.
  • They can only be attached on one virtual machine at a time; they must be detached from one machine before being attached to another.

StratusLab does not natively provide file or object-based storage services.


The primary commands for a persistent disks are:

$ stratus-create-volume --size ${GiB} --tag ${MY_DESC}
$ stratus-describe-volumes ${VOLUME_UUID}
$ stratus-update-volume [opts] ${VOLUME_UUID}
$ stratus-delete-volume ${VOLUME_UUID}

These commands create, describe (list), update metadata, and delete persistent disks, respectively.

The stratus-create-volume command takes the size of the volume in Gibibytes (GiB) and an optional tag. The tag is useful for remembering the contents of a given volume. A tag be added later with the stratus-update-volume command. This command returns the UUID of the created disk.

The stratus-describe-volumes command provides a list of persistent disks if no argument is provided. If you provide an argument, then the details for the given disk are provided. The --filter option is useful for limiting the number of disks returned in the list.


The StratusLab caching mechanism for virtual machine appliances uses the persistent disk infrastructure. When virtual machines are running you will see “snapshot” volumes corresponding to the root volumes for those machines.

The stratus-delete-volume deletes a given volume. This releases the allocated storage space and permanently deletes any stored data.


Once a persistent disk has been deleted, all of the data on the disk is deleted and cannot be recovered. Be certain that you reference the correct disk before deleting it!


Run through the entire persistent disk lifecycle with the command line interface. Try to change the tag associated with the disk after you’ve created it.


Create several (small) disks with different tags and sizes. Use the filtering to limit the information returned by the stratus-describe-volumes command.

Web Interface

There is also a web interface for this service which allows you to perform the same operations as you can from the command line. (It also allows you to see the current mount status of a disk which the command line client can’t do.)

You can discover the location of the web interface by pointing a browser at the URL for the “pdisk_endpoint” in your configuration (or at the “endpoint” value if “pdisk_endpoint” isn’t defined). Look for the “svc-pdisk.html” file in the listing.


That the web interface will change significantly in the coming releases.


Run through the entire persistent disk lifecycle though the web interface. Modify the tag (or add one) to an existing persistent disk.