267 lines
9.6 KiB
ReStructuredText
267 lines
9.6 KiB
ReStructuredText
===================================
|
|
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 a :command:`nova 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:
|
|
|
|
* :command:`lvm2` command. Directly manipulates the volumes.
|
|
|
|
* :command:`kpartx` command. Discovers the partition table created inside the
|
|
instance.
|
|
|
|
* :command:`tar` command. Creates a minimum-sized backup.
|
|
|
|
* :command:`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
|
|
|
|
.. code-block:: console
|
|
|
|
# lvdisplay
|
|
|
|
* Create the snapshot; you can do this while the volume is attached
|
|
to an instance:
|
|
|
|
.. code-block:: console
|
|
|
|
# lvcreate --size 10G --snapshot --name volume-00000001-snapshot \
|
|
/dev/cinder-volumes/volume-00000001
|
|
|
|
Use the :option:`--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 :option:`--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 :command:`lvdisplay` command again to verify the snapshot:
|
|
|
|
.. code-block:: console
|
|
|
|
--- 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 :command:`tar` command, mount
|
|
your partition on the Block Storage service server.
|
|
|
|
The :command:`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.
|
|
|
|
.. code-block:: console
|
|
|
|
# kpartx -av /dev/cinder-volumes/volume-00000001-snapshot
|
|
|
|
.. note::
|
|
|
|
On a Debian-based distribution, you can use the
|
|
:command:`apt-get install kpartx` command to install
|
|
:command:`kpartx`.
|
|
|
|
If the tools successfully find and map the partition table,
|
|
no errors are returned.
|
|
|
|
* To check the partition table map, run this command:
|
|
|
|
.. code-block:: console
|
|
|
|
$ 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
|
|
|
|
.. code-block:: console
|
|
|
|
# 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 :command:`kpartx`
|
|
command failed to discover the partition table.
|
|
|
|
Allocate more space to the snapshot and try the process again.
|
|
|
|
#. Use the :command:`tar` command to create archives
|
|
|
|
Create a backup of the volume:
|
|
|
|
.. code-block:: console
|
|
|
|
$ 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 I
|
|
|
|
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:
|
|
|
|
.. code-block:: console
|
|
|
|
$ sha1sum volume-00000001.tar.gz > volume-00000001.checksum
|
|
|
|
.. note::
|
|
|
|
Use the :command:`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.
|
|
|
|
.. code-block:: console
|
|
|
|
$ umount /mnt
|
|
|
|
* Delete the partition table.
|
|
|
|
.. code-block:: console
|
|
|
|
$ kpartx -dv /dev/cinder-volumes/volume-00000001-snapshot
|
|
|
|
* Remove the snapshot.
|
|
|
|
.. code-block:: console
|
|
|
|
$ 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:
|
|
|
|
.. code-block:: console
|
|
|
|
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
|
|
:command:`mysqldump` command into them. To make this work, enable
|
|
the connection to the Compute project keys. If you do not want to
|
|
run the :command:`mysqldump` command, you can add
|
|
``enable_mysql_dump=0`` to the script to turn off this functionality.
|
|
|
|
|
|
.. Links
|
|
.. _`SCR_5005_V01_NUAC-OPENSTACK-EBS-volumes-backup.sh`: https://github.com/Razique/BashStuff/blob/master/SYSTEMS/OpenStack/SCR_5005_V01_NUAC-OPENSTACK-EBS-volumes-backup.sh
|