e9857d616d
This patch is part of the docs migration for Cinder. It is more or less a drag and drop of the docs from openstack-manuals admin-guide directory. I needed to change some syntax to work with Cinder's more stringent doc build. Note that the purpose of this patch is just to get the documentation back to an accessible location. Later patches will clean up the organization and content. Change-Id: Ib3f9255e0f9f2ff42a0ee4126607ff319a3d901e
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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 an :command:`openstack volume create` command exist in an LVM
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logical 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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.. code-block:: console
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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 ``--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 ``/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 ``--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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.. code-block:: console
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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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.. code-block:: console
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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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.. code-block:: console
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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 ``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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.. code-block:: console
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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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Depending on your CPU, the process might take a long time for
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files larger than around 4 to 6 GB.
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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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.. code-block:: console
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$ umount /mnt
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* Delete the partition table.
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.. code-block:: console
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$ kpartx -dv /dev/cinder-volumes/volume-00000001-snapshot
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* Remove the snapshot.
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.. code-block:: console
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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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.. code-block:: console
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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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