########################################
Using EBS Volumes for Persistent Storage
########################################
StarCluster utilizes Amazon's Elastic Block Storage (EBS) volumes for
persistent storage. These volumes can be anywhere from 1GB to 1TB in size.
StarCluster will mount each volume specified in a cluster template to the
**MOUNT_PATH** specified in the volume's configuration section on the master
node. This **MOUNT_PATH** is then shared on all nodes using the network file
system (NFS).

For example, suppose we have the following (abbreviated) configuration defined:

.. code-block:: ini

    [vol myvol]
    volume_id = vol-v99999
    mount_path = /data

    [cluster smallcluster]
    cluster_size=3
    keyname=mykey
    node_instance_type=m1.small
    node_image_id=ami-8cf913e5
    volumes=myvol

In this case, whenever a cluster is launched using the *smallcluster* template
StarCluster will attach the EBS volume *vol-v99999* to the *master* node on
*/data* and then NFS-share */data* to all the nodes in the cluster.

**********************************
Create and Format a new EBS Volume
**********************************
StarCluster's **createvolume** command completely automates the process of
creating a new EBS volume. This includes launching a host instance in the
target zone, attaching the new volume to the host, and formatting the entire
volume.

.. warning::

    The **createvolume** command *only* supports formatting the *entire volume*
    using all of the space on the device. If you need multiple partitions
    you're probably better off creating multiple volumes instead. If this is
    not the case and you have a use-case for partitioning EBS volumes please
    send a note to the StarCluster mailing list (starcluster 'at' mit 'dot'
    edu).

To create and format a new volume simply specify a volume size (in GB) and the
zone you want to create the volume in::

    $ starcluster createvolume 20 us-east-1c

This command will launch a host instance in the us-east-1c availability zone,
create a 20GB volume in us-east-1c, attach the new volume to the host instance,
and format the entire volume.

You can also use the --bid option to request a spot instance when creating the
volume host::

    $ starcluster createvolume 20 us-east-1c --bid 0.50

.. warning::

    In previous versions the **createvolume** command used to terminate the
    host instance after creating the volume. **The latest version does not do
    this by default** in order to allow multiple volumes to be created in the
    same zone with a *single* host instance. You can pass the
    *--shutdown-volume-host* option to the *createvolume* command to have
    StarCluster automatically shutdown the volume host after creating the new
    volume.

Let's look at an example::

    $ starcluster createvolume 20 us-east-1c
    StarCluster - (http://web.mit.edu/starcluster)
    Software Tools for Academics and Researchers (STAR)
    Please submit bug reports to starcluster@mit.edu

    >>> No keypair specified, picking one from config...
    >>> Using keypair: jtriley
    >>> Creating security group @sc-volumecreator...
    >>> No instance in group @sc-volumecreator for zone us-east-1c,
    >>> launching one now.
    >>> Waiting for volume host to come up... (updating every 30s)
    >>> Waiting for open spot requests to become active...
    1/1 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||| 100%
    >>> Waiting for all nodes to be in a 'running' state...
    1/1 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||| 100%
    >>> Waiting for SSH to come up on all nodes...
    1/1 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||| 100%
    >>> Checking for required remote commands...
    >>> Creating 1GB volume in zone us-east-1c
    >>> New volume id: vol-2f3a5344
    >>> Waiting for new volume to become 'available'...
    >>> Attaching volume vol-2f3a5344 to instance i-fb9ceb95...
    >>> Formatting volume...
    mke2fs 1.41.11 (14-Mar-2010)
    Filesystem label=
    OS type: Linux
    Block size=4096 (log=2)
    Fragment size=4096 (log=2)
    Stride=0 blocks, Stripe width=0 blocks
    65536 inodes, 262144 blocks
    13107 blocks (5.00%) reserved for the super user
    First data block=0
    Maximum filesystem blocks=268435456
    8 block groups
    32768 blocks per group, 32768 fragments per group
    8192 inodes per group
    Superblock backups stored on blocks:
            32768, 98304, 163840, 229376

    Writing inode tables: done
    Creating journal (8192 blocks): done
    Writing superblocks and filesystem accounting information: done

    This filesystem will be automatically checked every 30 mounts or
    180 days, whichever comes first.  Use tune2fs -c or -i to override.
    >>> Leaving volume vol-2f3a5344 attached to instance i-fb9ceb95
    >>> Not terminating host instance i-fb9ceb95
    *** WARNING - There are still volume hosts running: i-fb9ceb95
    *** WARNING - Run 'starcluster terminate volumecreator' to terminate
    *** WARNING - *all* volume host instances once they're no longer needed
    >>> Creating volume took 7.396 mins
    >>> Your new 1GB volume vol-2f3a5344 has been created successfully

Notice the warning at the bottom of the above output. StarCluster will leave
the host instance running with the new volume attached after creating and
formatting the new volume. This allows multiple volumes to be created in a
given availability zone without launching a new instance for each volume. To
see the volume hosts simply run the *listclusters* command::

    $ starcluster listclusters volumecreator
    StarCluster - (http://web.mit.edu/starcluster)
    Software Tools for Academics and Researchers (STAR)
    Please submit bug reports to starcluster@mit.edu

    -------------------------------------------------
    volumecreator (security group: @sc-volumecreator)
    -------------------------------------------------
    Launch time: 2011-06-13 13:51:25
    Uptime: 00:02:09
    Zone: us-east-1c
    Keypair: mykey
    EBS volumes: N/A
    Cluster nodes:
        volhost-us-east-1c running i-fd9clb9z  (spot sir-2a8zb4lr)
    Total nodes: 1

From the above example we see that we have a volume-host in us-east-1c called
*volhost-us-east-1c*. Any volumes that were created will still be attached to
the volume host until you terminate the *volumecreator* cluster. If you'd
rather detach the volume after it's been successfully created use the
*--detach-volume* (-d) option::

    $ starcluster createvolume --detach-volume 20 us-east-1c

You can login to a volume host instance using::

    $ starcluster sshnode volumecreator volhost-us-east-1c

After logging in you can inspect the volume, upload data, etc.  When you're
done using the volumecreator cluster don't forget to terminate it::

    $ starcluster terminate volumecreator

If you'd rather avoid having to terminate the volumecreator each time you can
pass the *--shutdown-volume-host (-s)* option to the *createvolume* command to
have StarCluster automatically terminate the host-instance after successfully
creating the new volume::

    $ starcluster createvolume --shutdown-volume-host 20 us-east-1c

*************************************
Managing EBS Volumes with StarCluster
*************************************
In addition to creating and formatting new EBS volumes StarCluster also allows
you to browse and remove your EBS volumes.

Getting Volume Status
=====================
To get a list of all your volumes as well as their current status use the
**listvolumes** command::

    $ starcluster listvolumes

If you'd like to see details for a single volume::

    $ starcluster listvolumes -v vol-99999999

You can also filter the results by status::

    $ starcluster listvolumes -S available

and also by attachment state::

    $ starcluster listvolumes -a attached

Other filters are available, have a look at the help menu for more details::

    $ starcluster listvolumes --help

Removing Volumes
================
.. warning:: This process cannot be reversed!

To **permanently** remove an EBS volume use the *removevolume* command::

    $ starcluster removevolume vol-99999999

Resizing Volumes
================
After you've created and used an EBS volume over time you may find that you
need to add additional disk space to the EBS volume. Normally you would need to
snapshot the volume, create a new, larger, volume from the snapshot, attach the
new volume to an instance, and expand the filesystem to fit the new volume.
Fortunately, StarCluster's *resizevolume* command streamlines this process for
you.

.. note::

     The EBS volume must either be unpartitioned or contain only a single
     partition. Any other configuration will be aborted.

For example, to resize a 10GB volume, say vol-99999999, to 20GB::

    $ starcluster resizevolume vol-99999999 20

The above command will create a *new*, larger, 20GB volume containing the data
from the original volume vol-99999999. The new volume's filesystem will also be
expanded to fit the new volume size.

Just like the *createvolume* command, the *resizevolume* command will also
launch a host instance in order to attach the new volume and expand the
volume's filesystem. Similarly, if you wish to shutdown the host instance
automatically after the new resized volume has been created, use the
*--shutdown-volume-host* option::

    $ starcluster resizevolume --shutdown-volume-host vol-99999999 20

Otherwise, you will need to terminate the volume host manually after the
*resizevolume* command completes.

Moving Volumes Across Availability Zones
========================================
In some cases you may need to replicate a given volume to another availability
zone so that the data can be used with instances in a different data center.
The *resizevolume* command supports creating a newly expanded volume within an
alternate availability zone via the *-z*, or *--zone*, flag::

    $ starcluster resizevolume -z us-east-1d vol-9999999 20

The above command will create a new 20GB volume in us-east-1d containing the
data in vol-99999999. If you only want to move the volume data without resizing
simply specify the same size as the original volume.
