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01b_create_volumes.md

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This workshop will guide you through the creation and attachment of volumes.

Volumes can be seen as an external hard drive for your instances: they are virtual disks that you can attach to your instances to extend their storage capacity.

Pre-requisites: you need to have completed the first course and have booted two instances.

Create a volume

The creation of a volume is very simple, just issue the following command to create a 10GB volume:

openstack volume create --size 10 volume01

This will output some information about the newly created volume:

+---------------------+--------------------------------------+
| Field               | Value                                |
+---------------------+--------------------------------------+
| attachments         | []                                   |
| availability_zone   | nova                                 |
| bootable            | false                                |
| consistencygroup_id | None                                 |
| created_at          | 2019-01-03T14:07:04.298131           |
| description         | None                                 |
| encrypted           | False                                |
| id                  | 42c791f9-a84a-4034-b7cd-a1048054c50b |
| multiattach         | False                                |
| name                | volume01                             |
| properties          |                                      |
| replication_status  | disabled                             |
| size                | 10                                   |
| snapshot_id         | None                                 |
| source_volid        | None                                 |
| status              | creating                             |
| type                | classic                              |
| updated_at          | None                                 |
| user_id             | 12843a2...                           |
+---------------------+--------------------------------------+

Notice that the attachments list is empty so this volume is currently not attached just as an unplugged external hard drive. In this state it is not very useful.

You can run the following command to get back this information at a later time:

openstack volume show volume01

# Or with its id:
openstack volume show 42c791f9-a84a-4034-b7cd-a1048054c50b

Using the volume

Attach the volume to an instance

To be able to manipulate the volume you need to attach it to an instance. There is no need to shut down the instance prior the attachment so we will attach the volume on a live instance:

openstack server add volume myvm01 volume01

You can check that the attachment is effective by looking at the instance or at the volume:

openstack server show myvm01
# -> the ID of the volume is displayed in the volumes_attached property

openstack volume show volume01
# -> the attachments list now contains information about which instance it is attached to and the device that is used on the instance (/dev/sdb most likely)

Format and mount the volume

Connect to the instance you attached the volume to:

# With the ip of myvm01
ssh [email protected]

You can check the disks connected to the instance:

debian@myvm01:~$ lsblk

You should see a second disk on the instance:

NAME   MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda      8:0    0  20G  0 disk
└─sda1   8:1    0  20G  0 part /
sdb      8:16   0  10G  0 disk

The new disk (/dev/sdb here) is blank and does not have a partition nor a filesystem on it. So let's create one:

debian@myvm01:~$ echo 'start=2048, type=83' | sudo sfdisk /dev/sdb

This created a single partition starting at the offset 2048 and with a type 83 meaning Linux. Another run of lsblk should confirm there is now a partition on the volume:

NAME   MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda      8:0    0  20G  0 disk
└─sda1   8:1    0  20G  0 part /
sdb      8:16   0  10G  0 disk
└─sdb1   8:17   0  10G  0 part

Now we need to format it:

debian@myvm01:~$ sudo mkfs.ext4 /dev/sdb1

Finally we can mount it and use it:

debian@myvm01:~$ sudo mount /dev/sdb1 /mnt

And check the 10GB are there with df -h for instance:

Filesystem      Size  Used Avail Use% Mounted on
udev            1.9G     0  1.9G   0% /dev
tmpfs           386M   39M  348M  11% /run
/dev/sda1        20G 1016M   18G   6% /
tmpfs           1.9G     0  1.9G   0% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           1.9G     0  1.9G   0% /sys/fs/cgroup
/dev/sdb1       9.8G   37M  9.3G   1% /mnt

Now we add some data on the volume:

debian@myvm01:~$ echo "This is volume01" | sudo tee /mnt/content.txt

Move the volume to another instance

One of the benefits of a volume is that you can detach it and reattach it to another instance so let's do that.

But first you have to unmount the volume on myvm01:

debian@myvm01:~$ sudo umount /mnt

Now we can safely detach the volume:

openstack server remove volume myvm01 volume01

And reattach it to the other instance:

openstack server add volume myvm02 volume01

Now let's connect to myvm02:

# With the ip of myvm02
ssh [email protected]

Tip: you can see the IP of the instance with openstack server show myvm02

And check everything is there:

debian@myvm02:~$ lsblk
NAME   MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda      8:0    0  20G  0 disk
└─sda1   8:1    0  20G  0 part /
sdb      8:16   0  10G  0 disk
└─sdb1   8:17   0  10G  0 part
debian@myvm02:~$ sudo mount /dev/sdb1 /mnt
debian@myvm02:~$ cat /mnt/content.txt
This is volume01

You're up

Now you should be able to do the following tasks on your own:

  • ❗ Task 1: Detach volume01 from myvm02 and reattach it to myvm01
  • ❗ Task 2: Create a second volume: volume02
  • ❗ Task 3: Attach volume02 to myvm02 then partition it and format it
  • ❗ Task 4: Mount volume02 and add some content to it

Once you are ready, move on to the next course