mirror of https://github.com/ceph/ceph
324 lines
12 KiB
ReStructuredText
324 lines
12 KiB
ReStructuredText
===============
|
|
RBD Mirroring
|
|
===============
|
|
|
|
.. index:: Ceph Block Device; mirroring
|
|
|
|
RBD images can be asynchronously mirrored between two Ceph clusters. This
|
|
capability uses the RBD journaling image feature to ensure crash-consistent
|
|
replication between clusters. Mirroring is configured on a per-pool basis
|
|
within peer clusters and can be configured to automatically mirror all
|
|
images within a pool or only a specific subset of images. Mirroring is
|
|
configured using the ``rbd`` command. The ``rbd-mirror`` daemon is responsible
|
|
for pulling image updates from the remote, peer cluster and applying them to
|
|
the image within the local cluster.
|
|
|
|
.. note:: RBD mirroring requires the Ceph Jewel release or later.
|
|
|
|
.. important:: To use RBD mirroring, you must have two Ceph clusters, each
|
|
running the ``rbd-mirror`` daemon.
|
|
|
|
Pool Configuration
|
|
==================
|
|
|
|
The following procedures demonstrate how to perform the basic administrative
|
|
tasks to configure mirroring using the ``rbd`` command. Mirroring is
|
|
configured on a per-pool basis within the Ceph clusters.
|
|
|
|
The pool configuration steps should be performed on both peer clusters. These
|
|
procedures assume two clusters, named "local" and "remote", are accessible from
|
|
a single host for clarity.
|
|
|
|
See the `rbd`_ manpage for additional details of how to connect to different
|
|
Ceph clusters.
|
|
|
|
.. note:: The cluster name in the following examples corresponds to a Ceph
|
|
configuration file of the same name (e.g. /etc/ceph/remote.conf). See the
|
|
`ceph-conf`_ documentation for how to configure multiple clusters.
|
|
|
|
Enable Mirroring
|
|
----------------
|
|
|
|
To enable mirroring on a pool with ``rbd``, specify the ``mirror pool enable``
|
|
command, the pool name, and the mirroring mode::
|
|
|
|
rbd mirror pool enable {pool-name} {mode}
|
|
|
|
The mirroring mode can either be ``pool`` or ``image``:
|
|
|
|
* **pool**: When configured in ``pool`` mode, all images in the pool with the
|
|
journaling feature enabled are mirrored.
|
|
* **image**: When configured in ``image`` mode, mirroring needs to be
|
|
`explicitly enabled`_ on each image.
|
|
|
|
For example::
|
|
|
|
rbd --cluster local mirror pool enable image-pool pool
|
|
rbd --cluster remote mirror pool enable image-pool pool
|
|
|
|
Disable Mirroring
|
|
-----------------
|
|
|
|
To disable mirroring on a pool with ``rbd``, specify the ``mirror pool disable``
|
|
command and the pool name::
|
|
|
|
rbd mirror pool disable {pool-name}
|
|
|
|
When mirroring is disabled on a pool in this way, mirroring will also be
|
|
disabled on any images (within the pool) for which mirroring was enabled
|
|
explicitly.
|
|
|
|
For example::
|
|
|
|
rbd --cluster local mirror pool disable image-pool
|
|
rbd --cluster remote mirror pool disable image-pool
|
|
|
|
Add Cluster Peer
|
|
----------------
|
|
|
|
In order for the ``rbd-mirror`` daemon to discover its peer cluster, the peer
|
|
needs to be registered to the pool. To add a mirroring peer Ceph cluster with
|
|
``rbd``, specify the ``mirror pool peer add`` command, the pool name, and a
|
|
cluster specification::
|
|
|
|
rbd mirror pool peer add {pool-name} {client-name}@{cluster-name}
|
|
|
|
For example::
|
|
|
|
rbd --cluster local mirror pool peer add image-pool client.remote@remote
|
|
rbd --cluster remote mirror pool peer add image-pool client.local@local
|
|
|
|
Remove Cluster Peer
|
|
-------------------
|
|
|
|
To remove a mirroring peer Ceph cluster with ``rbd``, specify the
|
|
``mirror pool peer remove`` command, the pool name, and the peer UUID
|
|
(available from the ``rbd mirror pool info`` command)::
|
|
|
|
rbd mirror pool peer remove {pool-name} {peer-uuid}
|
|
|
|
For example::
|
|
|
|
rbd --cluster local mirror pool peer remove image-pool 55672766-c02b-4729-8567-f13a66893445
|
|
rbd --cluster remote mirror pool peer remove image-pool 60c0e299-b38f-4234-91f6-eed0a367be08
|
|
|
|
Data Pools
|
|
----------
|
|
|
|
When creating images in the destination cluster, ``rbd-mirror`` selects a data
|
|
pool as follows:
|
|
|
|
#. If the destination cluster has a default data pool configured (with the
|
|
``rbd_default_data_pool`` configuration option), it will be used.
|
|
#. Otherwise, if the source image uses a separate data pool, and a pool with the
|
|
same name exists on the destination cluster, that pool will be used.
|
|
#. If neither of the above is true, no data pool will be set.
|
|
|
|
Image Configuration
|
|
===================
|
|
|
|
Unlike pool configuration, image configuration only needs to be performed against
|
|
a single mirroring peer Ceph cluster.
|
|
|
|
Mirrored RBD images are designated as either primary or non-primary. This is a
|
|
property of the image and not the pool. Images that are designated as
|
|
non-primary cannot be modified.
|
|
|
|
Images are automatically promoted to primary when mirroring is first enabled on
|
|
an image (either implicitly if the pool mirror mode was **pool** and the image
|
|
has the journaling image feature enabled, or `explicitly enabled`_ by the
|
|
``rbd`` command).
|
|
|
|
Enable Image Journaling Support
|
|
-------------------------------
|
|
|
|
RBD mirroring uses the RBD journaling feature to ensure that the replicated
|
|
image always remains crash-consistent. Before an image can be mirrored to
|
|
a peer cluster, the journaling feature must be enabled. The feature can be
|
|
enabled at image creation time by providing the
|
|
``--image-feature exclusive-lock,journaling`` option to the ``rbd`` command.
|
|
|
|
Alternatively, the journaling feature can be dynamically enabled on
|
|
pre-existing RBD images. To enable journaling with ``rbd``, specify
|
|
the ``feature enable`` command, the pool and image name, and the feature name::
|
|
|
|
rbd feature enable {pool-name}/{image-name} {feature-name}
|
|
|
|
For example::
|
|
|
|
rbd --cluster local feature enable image-pool/image-1 journaling
|
|
|
|
.. note:: The journaling feature is dependent on the exclusive-lock feature. If
|
|
the exclusive-lock feature is not already enabled, it should be enabled prior
|
|
to enabling the journaling feature.
|
|
|
|
.. tip:: You can enable journaling on all new images by default by adding
|
|
``rbd default features = 125`` to your Ceph configuration file.
|
|
|
|
Enable Image Mirroring
|
|
----------------------
|
|
|
|
If the mirroring is configured in ``image`` mode for the image's pool, then it
|
|
is necessary to explicitly enable mirroring for each image within the pool.
|
|
To enable mirroring for a specific image with ``rbd``, specify the
|
|
``mirror image enable`` command along with the pool and image name::
|
|
|
|
rbd mirror image enable {pool-name}/{image-name}
|
|
|
|
For example::
|
|
|
|
rbd --cluster local mirror image enable image-pool/image-1
|
|
|
|
Disable Image Mirroring
|
|
-----------------------
|
|
|
|
To disable mirroring for a specific image with ``rbd``, specify the
|
|
``mirror image disable`` command along with the pool and image name::
|
|
|
|
rbd mirror image disable {pool-name}/{image-name}
|
|
|
|
For example::
|
|
|
|
rbd --cluster local mirror image disable image-pool/image-1
|
|
|
|
Image Promotion and Demotion
|
|
----------------------------
|
|
|
|
In a failover scenario where the primary designation needs to be moved to the
|
|
image in the peer Ceph cluster, access to the primary image should be stopped
|
|
(e.g. power down the VM or remove the associated drive from a VM), demote the
|
|
current primary image, promote the new primary image, and resume access to the
|
|
image on the alternate cluster.
|
|
|
|
.. note:: RBD only provides the necessary tools to facilitate an orderly
|
|
failover of an image. An external mechanism is required to coordinate the
|
|
full failover process (e.g. closing the image before demotion).
|
|
|
|
To demote a specific image to non-primary with ``rbd``, specify the
|
|
``mirror image demote`` command along with the pool and image name::
|
|
|
|
rbd mirror image demote {pool-name}/{image-name}
|
|
|
|
For example::
|
|
|
|
rbd --cluster local mirror image demote image-pool/image-1
|
|
|
|
To demote all primary images within a pool to non-primary with ``rbd``, specify
|
|
the ``mirror pool demote`` command along with the pool name::
|
|
|
|
rbd mirror pool demote {pool-name}
|
|
|
|
For example::
|
|
|
|
rbd --cluster local mirror pool demote image-pool
|
|
|
|
To promote a specific image to primary with ``rbd``, specify the
|
|
``mirror image promote`` command along with the pool and image name::
|
|
|
|
rbd mirror image promote [--force] {pool-name}/{image-name}
|
|
|
|
For example::
|
|
|
|
rbd --cluster remote mirror image promote image-pool/image-1
|
|
|
|
To promote all non-primary images within a pool to primary with ``rbd``, specify
|
|
the ``mirror pool promote`` command along with the pool name::
|
|
|
|
rbd mirror pool promote [--force] {pool-name}
|
|
|
|
For example::
|
|
|
|
rbd --cluster local mirror pool promote image-pool
|
|
|
|
.. tip:: Since the primary / non-primary status is per-image, it is possible to
|
|
have two clusters split the IO load and stage failover / failback.
|
|
|
|
.. note:: Promotion can be forced using the ``--force`` option. Forced
|
|
promotion is needed when the demotion cannot be propagated to the peer
|
|
Ceph cluster (e.g. Ceph cluster failure, communication outage). This will
|
|
result in a split-brain scenario between the two peers and the image will no
|
|
longer be in-sync until a `force resync command`_ is issued.
|
|
|
|
Force Image Resync
|
|
------------------
|
|
|
|
If a split-brain event is detected by the ``rbd-mirror`` daemon, it will not
|
|
attempt to mirror the affected image until corrected. To resume mirroring for an
|
|
image, first `demote the image`_ determined to be out-of-date and then request a
|
|
resync to the primary image. To request an image resync with ``rbd``, specify the
|
|
``mirror image resync`` command along with the pool and image name::
|
|
|
|
rbd mirror image resync {pool-name}/{image-name}
|
|
|
|
For example::
|
|
|
|
rbd mirror image resync image-pool/image-1
|
|
|
|
.. note:: The ``rbd`` command only flags the image as requiring a resync. The
|
|
local cluster's ``rbd-mirror`` daemon process is responsible for performing
|
|
the resync asynchronously.
|
|
|
|
Mirror Status
|
|
=============
|
|
|
|
The peer cluster replication status is stored for every primary mirrored image.
|
|
This status can be retrieved using the ``mirror image status`` and
|
|
``mirror pool status`` commands.
|
|
|
|
To request the mirror image status with ``rbd``, specify the
|
|
``mirror image status`` command along with the pool and image name::
|
|
|
|
rbd mirror image status {pool-name}/{image-name}
|
|
|
|
For example::
|
|
|
|
rbd mirror image status image-pool/image-1
|
|
|
|
To request the mirror pool summary status with ``rbd``, specify the
|
|
``mirror pool status`` command along with the pool name::
|
|
|
|
rbd mirror pool status {pool-name}
|
|
|
|
For example::
|
|
|
|
rbd mirror pool status image-pool
|
|
|
|
.. note:: Adding ``--verbose`` option to the ``mirror pool status`` command will
|
|
additionally output status details for every mirroring image in the pool.
|
|
|
|
rbd-mirror Daemon
|
|
=================
|
|
|
|
The two ``rbd-mirror`` daemons are responsible for watching image journals on the
|
|
remote, peer cluster and replaying the journal events against the local
|
|
cluster. The RBD image journaling feature records all modifications to the
|
|
image in the order they occur. This ensures that a crash-consistent mirror of
|
|
the remote image is available locally.
|
|
|
|
The ``rbd-mirror`` daemon is available within the optional ``rbd-mirror``
|
|
distribution package.
|
|
|
|
.. important:: Each ``rbd-mirror`` daemon requires the ability to connect
|
|
to both clusters simultaneously.
|
|
.. warning:: Pre-Luminous releases: only run a single ``rbd-mirror`` daemon per
|
|
Ceph cluster.
|
|
|
|
Each ``rbd-mirror`` daemon should use a unique Ceph user ID. To
|
|
`create a Ceph user`_, with ``ceph`` specify the ``auth get-or-create``
|
|
command, user name, monitor caps, and OSD caps::
|
|
|
|
ceph auth get-or-create client.rbd-mirror.{unique id} mon 'profile rbd' osd 'profile rbd'
|
|
|
|
The ``rbd-mirror`` daemon can be managed by ``systemd`` by specifying the user
|
|
ID as the daemon instance::
|
|
|
|
systemctl enable ceph-rbd-mirror@rbd-mirror.{unique id}
|
|
|
|
.. _rbd: ../../man/8/rbd
|
|
.. _ceph-conf: ../../rados/configuration/ceph-conf/#running-multiple-clusters
|
|
.. _explicitly enabled: #enable-image-mirroring
|
|
.. _force resync command: #force-image-resync
|
|
.. _demote the image: #image-promotion-and-demotion
|
|
.. _create a Ceph user: ../../rados/operations/user-management#add-a-user
|
|
|