Share replication

updated: 2021-01-20 19:21

Share replication

Replication of data has a number of use cases in the cloud. One use case is High Availability of the data in a shared file system, used for example, to support a production database. Another use case is ensuring Data Protection; i.e being prepared for a disaster by having a replication location that will be ready to back up your primary data source.

The Shared File System service supports user facing APIs that allow users to create shares that support replication, add and remove share replicas and manage their snapshots and access rules. Three replication types are currently supported and they vary in the semantics associated with the primary share and the secondary copies.

Important

Share replication is an experimental Shared File Systems API in the Mitaka release. Contributors can change or remove the experimental part of the Shared File Systems API in further releases without maintaining backward compatibility. Experimental APIs have an X-OpenStack-Manila-API-Experimental: true header in their HTTP requests.

Replication types supported

Before using share replication, make sure the Shared File System driver that you are running supports this feature. You can check it in the manila-scheduler service reports. The replication_type capability reported can have one of the following values:

writable
The driver supports creating writable share replicas. All share replicas can be accorded read/write access and would be synchronously mirrored.
readable
The driver supports creating read-only share replicas. All secondary share replicas can be accorded read access. Only the primary (or active share replica) can be written into.
dr
The driver supports creating dr (abbreviated from Disaster Recovery) share replicas. A secondary share replica is inaccessible until after a promotion.
None
The driver does not support Share Replication.

Note

The term active share replica refers to the primary share. In writable style of replication, all share replicas are active, and there could be no distinction of a primary share. In readable and dr styles of replication, a secondary share replica may be referred to as passive, non-active or simply, replica.

Configuration

Two new configuration options have been introduced to support Share Replication.

replica_state_update_interval
Specify this option in the DEFAULT section of your manila.conf. The Shared File Systems service requests periodic update of the replica_state of all non-active share replicas. The update occurs with respect to an interval corresponding to this option. If it is not specified, it defaults to 300 seconds.
replication_domain
Specify this option in the backend stanza when using a multi-backend style configuration. The value can be any ASCII string. Two backends that can replicate between each other would have the same replication_domain. This comes from the premise that the Shared File Systems service expects Share Replication to be performed between symmetric backends. This option is required for using the Share Replication feature.

Health of a share replica

Apart from the status attribute, share replicas have the replica_state attribute to denote the state of data replication on the storage backend. The primary share replica will have it’s replica_state attribute set to active. The secondary share replicas may have one of the following as their replica_state:

in_sync
The share replica is up to date with the active share replica (possibly within a backend-specific recovery point objective).
out_of_sync
The share replica is out of date (all new share replicas start out in this replica_state).
error
When the scheduler fails to schedule this share replica or some potentially irrecoverable error occurred with regard to updating data for this replica.

Promotion or failover

For readable and dr types of replication, we refer to the task of switching a non-active share replica with the active replica as promotion. For the writable style of replication, promotion does not make sense since all share replicas are active (or writable) at all times.

The status attribute of the non-active replica being promoted will be set to replication_change during its promotion. This has been classified as a busy state and thus API interactions with the share are restricted while one of its share replicas is in this state.

Share replication workflows

The following examples have been implemented with the ZFSonLinux driver that is a reference implementation in the Shared File Systems service. It operates in driver_handles_share_servers=False mode and supports the readable type of replication. In the example, we assume a configuration of two Availability Zones (configuration option: storage_availability_zone), called availability_zone_1 and availability_zone_2.

Multiple availability zones are not necessary to use the replication feature. However, the use of an availability zone as a failure domain is encouraged.

Pay attention to the network configuration for the ZFS driver. Here, we assume a configuration of zfs_service_ip and zfs_share_export_ip from two separate networks. The service network is reachable from the host where the manila-share service is running. The share export IP is from a network that allows user access.

See Configuring the ZFSonLinux driver for information on how to set up the ZFSonLinux driver.

Creating a share that supports replication

Create a new share type and specify the replication_type as an extra-spec within the share-type being used.

Use the manila type-create command to create a new share type. Specify the name and the value for the extra-spec driver_handles_share_servers.

$ manila type-create readable_type_replication False
+----------------------+--------------------------------------+
| Property             | Value                                |
+----------------------+--------------------------------------+
| required_extra_specs | driver_handles_share_servers : False |
| Name                 | readable_type_replication            |
| Visibility           | public                               |
| is_default           | -                                    |
| ID                   | 3b3ee3f7-6e43-4aa1-859d-0b0511c43074 |
| optional_extra_specs | snapshot_support : True              |
+----------------------+--------------------------------------+

Use the manila type-key command to set an extra-spec to the share type.

$ manila type-key readable_type_replication set replication_type=readable

Note

This command has no output. To verify the extra-spec, use the manila extra-specs-list command and specify the share type’s name or ID as a parameter.

Create a share with the share type

Use the manila create command to create a share. Specify the share protocol, size and the availability zone.

$ manila create NFS 1 --share_type readable_type_replication --name my_share --description "This share will have replicas" --az availability_zone_1
+-----------------------------+--------------------------------------+
| Property                    | Value                                |
+-----------------------------+--------------------------------------+
| status                      | creating                             |
| share_type_name             | readable_type_replication            |
| description                 | This share will have replicas        |
| availability_zone           | availability_zone_1                  |
| share_network_id            | None                                 |
| share_server_id             | None                                 |
| share_group_id              | None                                 |
| host                        |                                      |
| access_rules_status         | active                               |
| snapshot_id                 | None                                 |
| is_public                   | False                                |
| task_state                  | None                                 |
| snapshot_support            | True                                 |
| id                          | e496ed61-8f2e-436b-b299-32c3e90991cc |
| size                        | 1                                    |
| name                        | my_share                             |
| share_type                  | 3b3ee3f7-6e43-4aa1-859d-0b0511c43074 |
| has_replicas                | False                                |
| replication_type            | readable                             |
| created_at                  | 2016-03-29T20:22:18.000000           |
| share_proto                 | NFS                                  |
| project_id                  | 48a5ca76ac69405e99dc1c13c5195186     |
| metadata                    | {}                                   |
+-----------------------------+--------------------------------------+

Use the manila show command to retrieve details of the share. Specify the share ID or name as a parameter.

$ manila show my_share
+-----------------------------+--------------------------------------------------------------------+
| Property                    | Value                                                              |
+-----------------------------+--------------------------------------------------------------------+
| status                      | available                                                          |
| share_type_name             | readable_type_replication                                          |
| description                 | This share will have replicas                                      |
| availability_zone           | availability_zone_1                                                |
| share_network_id            | None                                                               |
| export_locations            |                                                                    |
|                             | path =                                                             |
|                             |10.32.62.26:/alpha/manila_share_38efc042_50c2_4825_a6d8_cba2a8277b28|
|                             | preferred = False                                                  |
|                             | is_admin_only = False                                              |
|                             | id = e1d754b5-ec06-42d2-afff-3e98c0013faf                          |
|                             | share_instance_id = 38efc042-50c2-4825-a6d8-cba2a8277b28           |
|                             | path =                                                             |
|                             |172.21.0.23:/alpha/manila_share_38efc042_50c2_4825_a6d8_cba2a8277b28|
|                             | preferred = False                                                  |
|                             | is_admin_only = True                                               |
|                             | id = 6f843ecd-a7ea-4939-86de-e1e01d9e8672                          |
|                             | share_instance_id = 38efc042-50c2-4825-a6d8-cba2a8277b28           |
| share_server_id             | None                                                               |
| share_group_id       | None                                                                     |
| host                        | openstack4@zfsonlinux_1#alpha                                      |
| access_rules_status         | active                                                             |
| snapshot_id                 | None                                                               |
| is_public                   | False                                                              |
| task_state                  | None                                                               |
| snapshot_support            | True                                                               |
| id                          | e496ed61-8f2e-436b-b299-32c3e90991cc                               |
| size                        | 1                                                                  |
| name                        | my_share                                                           |
| share_type                  | 3b3ee3f7-6e43-4aa1-859d-0b0511c43074                               |
| has_replicas                | False                                                              |
| replication_type            | readable                                                           |
| created_at                  | 2016-03-29T20:22:18.000000                                         |
| share_proto                 | NFS                                                                |
| project_id                  | 48a5ca76ac69405e99dc1c13c5195186                                   |
| metadata                    | {}                                                                 |
+-----------------------------+--------------------------------------------------------------------+

Note

When you create a share that supports replication, an active replica is created for you. You can verify this with the manila share-replica-list command.

Creating and promoting share replicas

Create a share replica

Use the manila share-replica-create command to create a share replica. Specify the share ID or name as a parameter. You may optionally provide the availability_zone and share_network_id. In the example below, share_network_id is not used since the ZFSonLinux driver does not support it.

$ manila share-replica-create my_share --az availability_zone_2
+-------------------+--------------------------------------+
| Property          | Value                                |
+-------------------+--------------------------------------+
| status            | creating                             |
| share_id          | e496ed61-8f2e-436b-b299-32c3e90991cc |
| availability_zone | availability_zone_2                  |
| created_at        | 2016-03-29T20:24:53.148992           |
| updated_at        | None                                 |
| share_network_id  | None                                 |
| share_server_id   | None                                 |
| host              |                                      |
| replica_state     | None                                 |
| id                | 78a5ef96-6c36-42e0-b50b-44efe7c1807e |
+-------------------+--------------------------------------+

See details of the newly created share replica

Use the manila share-replica-show command to see details of the newly created share replica. Specify the share replica’s ID as a parameter.

$ manila share-replica-show 78a5ef96-6c36-42e0-b50b-44efe7c1807e
+-------------------+--------------------------------------+
| Property          | Value                                |
+-------------------+--------------------------------------+
| status            | available                            |
| share_id          | e496ed61-8f2e-436b-b299-32c3e90991cc |
| availability_zone | availability_zone_2                  |
| created_at        | 2016-03-29T20:24:53.000000           |
| updated_at        | 2016-03-29T20:24:58.000000           |
| share_network_id  | None                                 |
| share_server_id   | None                                 |
| host              | openstack4@zfsonlinux_2#beta         |
| replica_state     | in_sync                              |
| id                | 78a5ef96-6c36-42e0-b50b-44efe7c1807e |
+-------------------+--------------------------------------+

See all replicas of the share

Use the manila share-replica-list command to see all the replicas of the share. Specify the share ID or name as an optional parameter.

$ manila share-replica-list --share-id my_share
+--------------------------------------+-----------+---------------+--------------------------------------+-------------------------------+---------------------+----------------------------+
| ID                                   | Status    | Replica State | Share ID                             | Host                          | Availability Zone   | Updated At                 |
+--------------------------------------+-----------+---------------+--------------------------------------+-------------------------------+---------------------+----------------------------+
| 38efc042-50c2-4825-a6d8-cba2a8277b28 | available | active        | e496ed61-8f2e-436b-b299-32c3e90991cc | openstack4@zfsonlinux_1#alpha | availability_zone_1 | 2016-03-29T20:22:19.000000 |
| 78a5ef96-6c36-42e0-b50b-44efe7c1807e | available | in_sync       | e496ed61-8f2e-436b-b299-32c3e90991cc | openstack4@zfsonlinux_2#beta  | availability_zone_2 | 2016-03-29T20:24:58.000000 |
+--------------------------------------+-----------+---------------+--------------------------------------+-------------------------------+---------------------+----------------------------+

Promote the secondary share replica to be the new active replica

Use the manila share-replica-promote command to promote a non-active share replica to become the active replica. Specify the non-active replica’s ID as a parameter.

$ manila share-replica-promote 78a5ef96-6c36-42e0-b50b-44efe7c1807e

Note

This command has no output.

The promotion may take time. During the promotion, the replica_state attribute of the share replica being promoted will be set to replication_change.

$ manila share-replica-list --share-id my_share
+--------------------------------------+-----------+--------------------+--------------------------------------+-------------------------------+---------------------+----------------------------+
| ID                                   | Status    |    Replica State   | Share ID                             | Host                          | Availability Zone   | Updated At                 |
+--------------------------------------+-----------+--------------------+--------------------------------------+-------------------------------+---------------------+----------------------------+
| 38efc042-50c2-4825-a6d8-cba2a8277b28 | available |       active       | e496ed61-8f2e-436b-b299-32c3e90991cc | openstack4@zfsonlinux_1#alpha | availability_zone_1 | 2016-03-29T20:32:19.000000 |
| 78a5ef96-6c36-42e0-b50b-44efe7c1807e | available | replication_change | e496ed61-8f2e-436b-b299-32c3e90991cc | openstack4@zfsonlinux_2#beta  | availability_zone_2 | 2016-03-29T20:32:19.000000 |
+--------------------------------------+-----------+--------------------+--------------------------------------+-------------------------------+---------------------+----------------------------+

Once the promotion is complete, the replica_state will be set to active.

$ manila share-replica-list --share-id my_share
+--------------------------------------+-----------+---------------+--------------------------------------+-------------------------------+---------------------+----------------------------+
| ID                                   | Status    | Replica State | Share ID                             | Host                          | Availability Zone   | Updated At                 |
+--------------------------------------+-----------+---------------+--------------------------------------+-------------------------------+---------------------+----------------------------+
| 38efc042-50c2-4825-a6d8-cba2a8277b28 | available | in_sync       | e496ed61-8f2e-436b-b299-32c3e90991cc | openstack4@zfsonlinux_1#alpha | availability_zone_1 | 2016-03-29T20:32:19.000000 |
| 78a5ef96-6c36-42e0-b50b-44efe7c1807e | available | active        | e496ed61-8f2e-436b-b299-32c3e90991cc | openstack4@zfsonlinux_2#beta  | availability_zone_2 | 2016-03-29T20:32:19.000000 |
+--------------------------------------+-----------+---------------+--------------------------------------+-------------------------------+---------------------+----------------------------+

Access rules

Create an IP access rule for the share

Use the manila access-allow command to add an access rule. Specify the share ID or name, protocol and the target as parameters.

$ manila access-allow my_share ip 0.0.0.0/0 --access-level rw
+--------------+--------------------------------------+
| Property     | Value                                |
+--------------+--------------------------------------+
| share_id     | e496ed61-8f2e-436b-b299-32c3e90991cc |
| access_type  | ip                                   |
| access_to    | 0.0.0.0/0                            |
| access_level | rw                                   |
| state        | new                                  |
| id           | 8b339cdc-c1e0-448f-bf6d-f068ee6e8f45 |
+--------------+--------------------------------------+

Note

Access rules are not meant to be different across the replicas of the share. However, as per the type of replication, drivers may choose to modify the access level prescribed. In the above example, even though read/write access was requested for the share, the driver will provide read-only access to the non-active replica to the same target, because of the semantics of the replication type: readable. However, the target will have read/write access to the (currently) non-active replica when it is promoted to become the active replica.

The manila access-deny command can be used to remove a previously applied access rule.

List the export locations of the share

Use the manila share-export-locations-list command to list the export locations of a share.

$ manila share-export-location-list my_share
+--------------------------------------+---------------------------------------------------------------------------+-----------+
| ID                                   | Path                                                                      | Preferred |
+--------------------------------------+---------------------------------------------------------------------------+-----------+
| 3ed3fbf5-2fa1-4dc0-8440-a0af72398cb6 | 10.32.62.21:/beta/subdir/manila_share_78a5ef96_6c36_42e0_b50b_44efe7c1807e| False     |
| 6f843ecd-a7ea-4939-86de-e1e01d9e8672 | 172.21.0.23:/alpha/manila_share_38efc042_50c2_4825_a6d8_cba2a8277b28      | False     |
| e1d754b5-ec06-42d2-afff-3e98c0013faf | 10.32.62.26:/alpha/manila_share_38efc042_50c2_4825_a6d8_cba2a8277b28      | False     |
| f3c5585f-c2f7-4264-91a7-a4a1e754e686 | 172.21.0.29:/beta/subdir/manila_share_78a5ef96_6c36_42e0_b50b_44efe7c1807e| False     |
+--------------------------------------+---------------------------------------------------------------------------+-----------+

Identify the export location corresponding to the share replica on the user accessible network and you may mount it on the target node.

Note

As an administrator, you can list the export locations for a particular share replica by using the manila share-instance-export-location-list command and specifying the share replica’s ID as a parameter.

Snapshots

Create a snapshot of the share

Use the manila snapshot-create command to create a snapshot of the share. Specify the share ID or name as a parameter.

$ manila snapshot-create my_share --name "my_snapshot"
+-------------------+--------------------------------------+
| Property          | Value                                |
+-------------------+--------------------------------------+
| status            | creating                             |
| share_id          | e496ed61-8f2e-436b-b299-32c3e90991cc |
| description       | None                                 |
| created_at        | 2016-03-29T21:14:03.000000           |
| share_proto       | NFS                                  |
| provider_location | None                                 |
| id                | 06cdccaf-93a0-4e57-9a39-79fb1929c649 |
| size              | 1                                    |
| share_size        | 1                                    |
| name              | my_snapshot                          |
+-------------------+--------------------------------------+

Show the details of the snapshot

Use the manila snapshot-show to view details of a snapshot. Specify the snapshot ID or name as a parameter.

$ manila snapshot-show my_snapshot
+-------------------+--------------------------------------+
| Property          | Value                                |
+-------------------+--------------------------------------+
| status            | available                            |
| share_id          | e496ed61-8f2e-436b-b299-32c3e90991cc |
| description       | None                                 |
| created_at        | 2016-03-29T21:14:03.000000           |
| share_proto       | NFS                                  |
| provider_location | None                                 |
| id                | 06cdccaf-93a0-4e57-9a39-79fb1929c649 |
| size              | 1                                    |
| share_size        | 1                                    |
| name              | my_snapshot                          |
+-------------------+--------------------------------------+

Note

The status attribute of a snapshot will transition from creating to available only when it is present on all the share replicas that have their replica_state attribute set to active or in_sync.

Likewise, the replica_state attribute of a share replica will transition from out_of_sync to in_sync only when all available snapshots are present on it.

Planned failovers

As an administrator, you can use the manila share-replica-resync command to attempt to sync data between active and non-active share replicas of a share before promotion. This will ensure that share replicas have the most up-to-date data and their relationships can be safely switched.

$ manila share-replica-resync 38efc042-50c2-4825-a6d8-cba2a8277b28

Note

This command has no output.

Updating attributes

If an error occurs while updating data or replication relationships (during a promotion), the Shared File Systems service may not be able to determine the consistency or health of a share replica. It may require administrator intervention to make any fixes on the storage backend as necessary. In such a situation, state correction within the Shared File Systems service is possible.

As an administrator, you can:

Reset the status attribute of a share replica

Use the manila share-replica-reset-state command to reset the status attribute. Specify the share replica’s ID as a parameter and use the --state option to specify the state intended.

$ manila share-replica-reset-state 38efc042-50c2-4825-a6d8-cba2a8277b28 --state=available

Note

This command has no output.

Reset the replica_state attribute

Use the manila share-replica-reset-replica-state command to reset the replica_state attribute. Specify the share replica’s ID and use the --state option to specify the state intended.

$ manila share-replica-reset-replica-state 38efc042-50c2-4825-a6d8-cba2a8277b28 --state=out_of_sync

Note

This command has no output.

Force delete a specified share replica in any state

Use the manila share-replica-delete command with the ‘–force’ key to remove the share replica, regardless of the state it is in.

$ manila share-replica-show 9513de5d-0384-4528-89fb-957dd9b57680
+-------------------+--------------------------------------+
| Property          | Value                                |
+-------------------+--------------------------------------+
| status            | error                                |
| share_id          | e496ed61-8f2e-436b-b299-32c3e90991cc |
| availability_zone | availability_zone_1                  |
| created_at        | 2016-03-30T01:32:47.000000           |
| updated_at        | 2016-03-30T01:34:25.000000           |
| share_network_id  | None                                 |
| share_server_id   | None                                 |
| host              | openstack4@zfsonlinux_1#alpha        |
| replica_state     | out_of_sync                          |
| id                | 38efc042-50c2-4825-a6d8-cba2a8277b28 |
+-------------------+--------------------------------------+

$ manila share-replica-delete --force 38efc042-50c2-4825-a6d8-cba2a8277b28

Note

This command has no output.

Use the policy.json file to grant permissions for these actions to other roles.

Deleting share replicas

Use the manila share-replica-delete command with the share replica’s ID to delete a share replica.

$ manila share-replica-delete 38efc042-50c2-4825-a6d8-cba2a8277b28

Note

This command has no output.

Note

You cannot delete the last active replica with this command. You should use the manila delete command to remove the share.

updated: 2021-01-20 19:21
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