c5a2b42cb2
Fix header typo, miscellaneous RST formatting. Change-Id: I0f7f6890fe100a79c27e328906f46375b3238f91
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===================================
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Back up Block Storage service disks
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===================================
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While you can use the LVM snapshot to create snapshots, you can also use
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it to back up your volumes. By using LVM snapshot, you reduce the size
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of the backup; only existing data is backed up instead of the entire
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volume.
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To back up a volume, you must create a snapshot of it. An LVM snapshot
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is the exact copy of a logical volume, which contains data in a frozen
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state. This prevents data corruption, because data cannot be manipulated
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during the volume creation process. Remember that the volumes created
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through a :command:`nova volume-create` command exist in an LVM logical
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volume.
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You must also make sure that the operating system is not using the
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volume, and that all data has been flushed on the guest file systems.
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This usually means that those file systems have to be unmounted during
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the snapshot creation. They can be mounted again as soon as the logical
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volume snapshot has been created.
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Before you create the snapshot, you must have enough space to save it.
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As a precaution, you should have at least twice as much space as the
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potential snapshot size. If insufficient space is available, the snapshot
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might become corrupted.
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For this example, assume that a 100 GB volume named ``volume-00000001``
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was created for an instance while only 4 GB are used. This example uses
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these commands to back up only those 4 GB:
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* :command:`lvm2` command. Directly manipulates the volumes.
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* :command:`kpartx` command. Discovers the partition table created inside the
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instance.
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* :command:`tar` command. Creates a minimum-sized backup.
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* :command:`sha1sum` command. Calculates the backup checksum to check its
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consistency.
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You can apply this process to volumes of any size.
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**To back up Block Storage service disks**
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#. Create a snapshot of a used volume
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* Use this command to list all volumes
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.. code-block:: console
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# lvdisplay
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* Create the snapshot; you can do this while the volume is attached
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to an instance::
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# lvcreate --size 10G --snapshot --name volume-00000001-snapshot \
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/dev/cinder-volumes/volume-00000001
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Use the :option:`--snapshot` configuration option to tell LVM that you want a
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snapshot of an already existing volume. The command includes the size
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of the space reserved for the snapshot volume, the name of the snapshot,
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and the path of an already existing volume. Generally, this path
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is :file:`/dev/cinder-volumes/VOLUME_NAME`.
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The size does not have to be the same as the volume of the snapshot.
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The :option:`--size` parameter defines the space that LVM reserves
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for the snapshot volume. As a precaution, the size should be the same
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as that of the original volume, even if the whole space is not
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currently used by the snapshot.
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* Run the :command:`lvdisplay` command again to verify the snapshot::
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--- Logical volume ---
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LV Name /dev/cinder-volumes/volume-00000001
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VG Name cinder-volumes
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LV UUID gI8hta-p21U-IW2q-hRN1-nTzN-UC2G-dKbdKr
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LV Write Access read/write
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LV snapshot status source of
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/dev/cinder-volumes/volume-00000026-snap [active]
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LV Status available
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# open 1
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LV Size 15,00 GiB
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Current LE 3840
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Segments 1
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Allocation inherit
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Read ahead sectors auto
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- currently set to 256
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Block device 251:13
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--- Logical volume ---
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LV Name /dev/cinder-volumes/volume-00000001-snap
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VG Name cinder-volumes
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LV UUID HlW3Ep-g5I8-KGQb-IRvi-IRYU-lIKe-wE9zYr
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LV Write Access read/write
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LV snapshot status active destination for /dev/cinder-volumes/volume-00000026
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LV Status available
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# open 0
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LV Size 15,00 GiB
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Current LE 3840
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COW-table size 10,00 GiB
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COW-table LE 2560
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Allocated to snapshot 0,00%
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Snapshot chunk size 4,00 KiB
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Segments 1
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Allocation inherit
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Read ahead sectors auto
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- currently set to 256
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Block device 251:14
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#. Partition table discovery
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* To exploit the snapshot with the :command:`tar` command, mount
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your partition on the Block Storage service server.
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The :command:`kpartx` utility discovers and maps table partitions.
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You can use it to view partitions that are created inside the
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instance. Without using the partitions created inside instances,
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you cannot see its content and create efficient backups.
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.. code-block::console
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# kpartx -av /dev/cinder-volumes/volume-00000001-snapshot
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.. note::
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On a Debian-based distribution, you can use the
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:command:`apt-get install kpartx` command to install
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:command:`kpartx`.
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If the tools successfully find and map the partition table,
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no errors are returned.
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* To check the partition table map, run this command::
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$ ls /dev/mapper/nova*
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You can see the ``cinder--volumes-volume--00000001--snapshot1``
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partition.
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If you created more than one partition on that volume, you see
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several partitions; for example:
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``cinder--volumes-volume--00000001--snapshot2``,
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``cinder--volumes-volume--00000001--snapshot3``, and so on.
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* Mount your partition
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.. code-block:: console
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# mount /dev/mapper/cinder--volumes-volume--volume--00000001--snapshot1 /mnt
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If the partition mounts successfully, no errors are returned.
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You can directly access the data inside the instance. If a message
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prompts you for a partition or you cannot mount it, determine whether
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enough space was allocated for the snapshot or the :command:`kpartx`
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command failed to discover the partition table.
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Allocate more space to the snapshot and try the process again.
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#. Use the :command:`tar` command to create archives
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Create a backup of the volume::
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$ tar --exclude="lost+found" --exclude="some/data/to/exclude" -czf \
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volume-00000001.tar.gz -C /mnt/ /backup/destination
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This command creates a :file:`tar.gz` file that contains the data,
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*and data only*. This ensures that you do not waste space by backing
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up empty sectors.
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#. Checksum calculation I
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You should always have the checksum for your backup files. When you
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transfer the same file over the network, you can run a checksum
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calculation to ensure that your file was not corrupted during its
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transfer. The checksum is a unique ID for a file. If the checksums are
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different, the file is corrupted.
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Run this command to run a checksum for your file and save the result
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to a file::
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$ sha1sum volume-00000001.tar.gz > volume-00000001.checksum
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.. note::
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Use the :command:`sha1sum` command carefully because the time it
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takes to complete the calculation is directly proportional to the
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size of the file.
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For files larger than around 4 to 6 GB, and depending on your CPU,
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the process might take a long time.
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#. After work cleaning
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Now that you have an efficient and consistent backup, use this command
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to clean up the file system:
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* Unmount the volume::
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$ umount /mnt
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* Delete the partition table::
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$ kpartx -dv /dev/cinder-volumes/volume-00000001-snapshot
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* Remove the snapshot::
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$ lvremove -f /dev/cinder-volumes/volume-00000001-snapshot
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Repeat these steps for all your volumes.
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#. Automate your backups
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Because more and more volumes might be allocated to your Block Storage
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service, you might want to automate your backups.
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The `SCR_5005_V01_NUAC-OPENSTACK-EBS-volumes-backup.sh`_ script assists
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you with this task. The script performs the operations from the previous
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example, but also provides a mail report and runs the backup based on
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the ``backups_retention_days`` setting.
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Launch this script from the server that runs the Block Storage service.
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This example shows a mail report::
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Backup Start Time - 07/10 at 01:00:01
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Current retention - 7 days
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The backup volume is mounted. Proceed...
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Removing old backups... : /BACKUPS/EBS-VOL/volume-00000019/volume-00000019_28_09_2011.tar.gz
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/BACKUPS/EBS-VOL/volume-00000019 - 0 h 1 m and 21 seconds. Size - 3,5G
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The backup volume is mounted. Proceed...
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Removing old backups... : /BACKUPS/EBS-VOL/volume-0000001a/volume-0000001a_28_09_2011.tar.gz
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/BACKUPS/EBS-VOL/volume-0000001a - 0 h 4 m and 15 seconds. Size - 6,9G
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---------------------------------------
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Total backups size - 267G - Used space : 35%
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Total execution time - 1 h 75 m and 35 seconds
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The script also enables you to SSH to your instances and run a
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:command:`mysqldump` command into them. To make this work, enable
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the connection to the Compute project keys. If you do not want to
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run the :command:`mysqldump` command, you can add
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``enable_mysql_dump=0`` to the script to turn off this functionality.
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.. Links
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.. _`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
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