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
writableshare replicas. All share replicas can be accorded read/write access and would be synchronously mirrored.- readable
The driver supports creating
read-onlyshare replicas. All secondary share replicas can be accorded read access. Only the primary (oractiveshare 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 apromotion.- 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
DEFAULTsection of yourmanila.conf. The Shared File Systems service requests periodic update of the replica_state of allnon-activeshare 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
activeshare replica (possibly within a backend-specificrecovery 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 [1],
called availability_zone_1 and availability_zone_2.
Since the Train release, some drivers operating in
driver_handles_share_server=True mode support share replication.
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 | {} |
+-----------------------------+--------------------------------------+
Note
If you are creating a share with the share type specification
driver_handles_share_servers=True, the share network parameter is
required for the operation to be performed.
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.
From API version 2.53, when creating a replicated share, the manila quota
system will reserve and consume resources for two additional quotas:
share_replicas and replica_gigabytes.
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 or the scheduler_hints.
For the scheduler hints, the value of only_host parameter must be a
manila-share service host in host@backend#POOL format.
$ manila share-replica-create my_share --az availability_zone_2 --scheduler_hints only_host=openstack4@zfsonlinux_2#beta
+-------------------+--------------------------------------+
| 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
Note
Since API version 2.51 (Train release), a share network is able to span
multiple subnets in different availability zones. So, when using a share
type with specification driver_handles_share_servers=True, users must
ensure that the share network has a subnet in the availability zone that
they desire the share replica to be created in.
Note
Scheduler hints are available only for API version >= 2.67.
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 |
| user_id | 5c7bdb6eb0504d54a619acf8375c08ce |
| description | None |
| created_at | 2016-03-29T21:14:03.000000 |
| share_proto | NFS |
| provider_location | None |
| id | 06cdccaf-93a0-4e57-9a39-79fb1929c649 |
| project_id | cadd7139bc3148b8973df097c0911016 |
| 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 |
| user_id | 5c7bdb6eb0504d54a619acf8375c08ce |
| description | None |
| created_at | 2016-03-29T21:14:03.000000 |
| share_proto | NFS |
| provider_location | None |
| id | 06cdccaf-93a0-4e57-9a39-79fb1929c649 |
| project_id | cadd7139bc3148b8973df097c0911016 |
| 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.yaml 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.
