Back up Block Storage service disks

While you can use the LVM snapshot to create snapshots, you can also
use it to back up your volumes. By using LVM snapshot, you reduce the
size of the backup; only existing data is backed up instead of the
entire volume.

To back up a volume, you must create a snapshot of it. An LVM
snapshot is the exact copy of a logical volume, which contains data in a
frozen state. This prevents data corruption because data cannot be
manipulated during the volume creation process. Remember that the
volumes created through an openstack volume create command exist in an LVM
logical volume.

You must also make sure that the operating system is not using the
volume and that all data has been flushed on the guest file systems.
This usually means that those file systems have to be unmounted during
the snapshot creation. They can be mounted again as soon as the logical
volume snapshot has been created.

Before you create the snapshot you must have enough space to save it.
As a precaution, you should have at least twice as much space as the
potential snapshot size. If insufficient space is available, the
snapshot might become corrupted.

For this example assume that a 100 GB volume named
volume-00000001 was created for an instance while only 4 GB
are used. This example uses these commands to back up only those 4
GB:

lvm2 command.
Directly manipulates the volumes.
kpartx command.
Discovers the partition table created inside the instance.
tar command.
Creates a minimum-sized backup.
sha1sum
command. Calculates the backup checksum to check its consistency.

You can apply this process to volumes of any size.

To back up Block Storage service disks

Create a snapshot of a used volume

Use this command to list all volumes
```
# lvdisplay
```
Create the snapshot; you can do this while the volume is attached
to an instance:
```
# lvcreate --size 10G --snapshot --name volume-00000001-snapshot \
  /dev/cinder-volumes/volume-00000001
```
Use the --snapshot configuration option to tell LVM that
you want a snapshot of an already existing volume. The command includes
the size of the space reserved for the snapshot volume, the name of the
snapshot, and the path of an already existing volume. Generally, this
path is /dev/cinder-volumes/VOLUME_NAME.

The size does not have to be the same as the volume of the snapshot.
The --size parameter defines the space that LVM reserves
for the snapshot volume. As a precaution, the size should be the same as
that of the original volume, even if the whole space is not currently
used by the snapshot.

Run the lvdisplay command again to verify the
snapshot:

--- Logical volume ---
LV Name                /dev/cinder-volumes/volume-00000001
VG Name                cinder-volumes
LV UUID                gI8hta-p21U-IW2q-hRN1-nTzN-UC2G-dKbdKr
LV Write Access        read/write
LV snapshot status     source of
                       /dev/cinder-volumes/volume-00000026-snap [active]
LV Status              available
# open                 1
LV Size                15,00 GiB
Current LE             3840
Segments               1
Allocation             inherit
Read ahead sectors     auto
- currently set to     256
Block device           251:13

--- Logical volume ---
LV Name                /dev/cinder-volumes/volume-00000001-snap
VG Name                cinder-volumes
LV UUID                HlW3Ep-g5I8-KGQb-IRvi-IRYU-lIKe-wE9zYr
LV Write Access        read/write
LV snapshot status     active destination for /dev/cinder-volumes/volume-00000026
LV Status              available
# open                 0
LV Size                15,00 GiB
Current LE             3840
COW-table size         10,00 GiB
COW-table LE           2560
Allocated to snapshot  0,00%
Snapshot chunk size    4,00 KiB
Segments               1
Allocation             inherit
Read ahead sectors     auto
- currently set to     256
Block device           251:14

Partition table discovery
- To exploit the snapshot with the tar command, mount your partition on the Block
  Storage service server.
  
  The kpartx
  utility discovers and maps table partitions. You can use it to view
  partitions that are created inside the instance. Without using the
  partitions created inside instances, you cannot see its content and
  create efficient backups.
```
# kpartx -av /dev/cinder-volumes/volume-00000001-snapshot
```
  Note
  
  On a Debian-based distribution, you can use the apt-get install kpartx
  command to install kpartx.
  
  If the tools successfully find and map the partition table, no errors
  are returned.
- To check the partition table map, run this command:
```
$ ls /dev/mapper/nova*
```
  You can see the
  cinder--volumes-volume--00000001--snapshot1 partition.
  
  If you created more than one partition on that volume, you see
  several partitions; for example:
  cinder--volumes-volume--00000001--snapshot2,
  cinder--volumes-volume--00000001--snapshot3, and so
  on.
- Mount your partition
```
# mount /dev/mapper/cinder--volumes-volume--volume--00000001--snapshot1 /mnt
```
  If the partition mounts successfully, no errors are returned.
  
  You can directly access the data inside the instance. If a message
  prompts you for a partition or you cannot mount it, determine whether
  enough space was allocated for the snapshot or the kpartx command failed to
  discover the partition table.
  
  Allocate more space to the snapshot and try the process
  again.
Use the tar
command to create archives

Create a backup of the volume:
```
$ tar --exclude="lost+found" --exclude="some/data/to/exclude" -czf \
  volume-00000001.tar.gz -C /mnt/ /backup/destination
```
This command creates a tar.gz file that contains the
data, and data only. This ensures that you do not waste space
by backing up empty sectors.
Checksum calculation

You should always have the checksum for your backup files. When you
transfer the same file over the network, you can run a checksum
calculation to ensure that your file was not corrupted during its
transfer. The checksum is a unique ID for a file. If the checksums are
different, the file is corrupted.

Run this command to run a checksum for your file and save the result
to a file:
```
$ sha1sum volume-00000001.tar.gz > volume-00000001.checksum
```
Note

Use the sha1sum
command carefully because the time it takes to complete the calculation
is directly proportional to the size of the file.

Depending on your CPU, the process might take a long time for files
larger than around 4 to 6 GB.
After work cleaning

Now that you have an efficient and consistent backup, use this
command to clean up the file system:
- Unmount the volume.
```
$ umount /mnt
```
- Delete the partition table.
```
$ kpartx -dv /dev/cinder-volumes/volume-00000001-snapshot
```
- Remove the snapshot.
```
$ lvremove -f /dev/cinder-volumes/volume-00000001-snapshot
```
Repeat these steps for all your volumes.
Automate your backups

Because more and more volumes might be allocated to your Block
Storage service, you might want to automate your backups. The SCR_5005_V01_NUAC-OPENSTACK-EBS-volumes-backup.sh
script assists you with this task. The script performs the operations
from the previous example, but also provides a mail report and runs the
backup based on the backups_retention_days setting.

Launch this script from the server that runs the Block Storage
service.

This example shows a mail report:
```
Backup Start Time - 07/10 at 01:00:01
Current retention - 7 days

The backup volume is mounted. Proceed...
Removing old backups...  : /BACKUPS/EBS-VOL/volume-00000019/volume-00000019_28_09_2011.tar.gz
     /BACKUPS/EBS-VOL/volume-00000019 - 0 h 1 m and 21 seconds. Size - 3,5G

The backup volume is mounted. Proceed...
Removing old backups...  : /BACKUPS/EBS-VOL/volume-0000001a/volume-0000001a_28_09_2011.tar.gz
     /BACKUPS/EBS-VOL/volume-0000001a - 0 h 4 m and 15 seconds. Size - 6,9G
---------------------------------------
Total backups size - 267G - Used space : 35%
Total execution time - 1 h 75 m and 35 seconds
```
The script also enables you to SSH to your instances and run a mysqldump command into
them. To make this work, enable the connection to the Compute project
keys. If you do not want to run the mysqldump command, you can add
enable_mysql_dump=0 to the script to turn off this
functionality.

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Back up Block Storage service disks

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