Converting a Metro Mirror consistency group to a 3-site consistency group

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Before you convert an in-production 2-site Metro Mirror consistency group to a 3-site consistency group, verify the state of the consistency group.

Consider the following information:

The Metro Mirror consistency group must be in the Consistent synchronized (3site_consistent) state.
Ensure that a storage pool is configured with enough capacity on the system at the auxiliary-far site. Typically, the target pools at the auxiliary-far site must have at least as much capacity as the current pools in the 2-site consistency group. If the storage pool at the auxiliary-far site does not have enough capacity, copy operations might fail.

Using the management GUI

On the 3-Site Partnership page, select the Convert 2-site consistency group to display Metro Mirror consistency groups between the systems at the master and auxiliary-near sites that are in the Consistent synchronized state. However, if no Metro Mirror consistency groups can be converted, you need to create a Metro Mirror consistency group, add relationships, and ensure that the group is synchronized before you can convert it to a 3-site consistency group.

To create a 2-site consistency group, complete these steps:

In the management GUI, select Copy Services > Remote Copy.
Click Add Consistency Group.
Enter a name for the consistency group and select the system at the auxiliary-near site. Click Add.
Under Partnerships, select the system at the auxiliary-near site to display the new, empty consistency group between the systems at the master and auxiliary-near sites. You can add an existing independent relationship to the new consistency group:
To add an existing independent relationship, complete these steps:
1. On the Remote Copy page, select the Independent Relationships tab.
2. Right-click the relationship and select Add to Consistency Group.
3. On the Add Relationship to Consistency Group page, select the new consistency group.
Verify that the 2-site consistency group is Consistent synchronized. If it is not, start the consistency group by selecting Actions > Start group.

After the relationships are assigned to the 2-site consistency group, you can convert it to a 3-site consistency group. As part of the conversion process, you need to specify the identifier of the pool that provides capacity for the target volumes on the system at the auxiliary-far site. The pool must exist on the system at the auxiliary-far site and have enough capacity to ensure that conversion completes successfully. Before you complete the conversion, verify that the specified pool has sufficient capacity. Capacity reporting can be complex and potentially inaccurate when different pool types are used in the consistency groups. Accurate capacity reporting requires appropriate planning and monitoring to ensure that out-of-space conditions do not occur. IBM® Storage Insights provides management tools that monitor capacity for your storage.

After the relationships are assigned to the 2-site consistency group, you can convert it to a 3-site consistency group. As part of the conversion process, you need to specify the identifier of the pool that provides capacity for the target volumes on the system at the auxiliary-far site. The pool must exist on the system at the auxiliary-far site and have enough capacity to ensure that conversion completes successfully. Before you complete the conversion, verify that the specified pool has sufficient capacity. Capacity reporting can be complex and potentially inaccurate when different pool types are used in the consistency groups. Accurate capacity reporting requires appropriate planning and monitoring to ensure that out-of-space conditions do not occur. IBM Storage Insights provides management tools that monitor capacity for your storage.

To convert an existing 2-site consistency group, complete these steps:

On the 3-Site Partnership page, select the Convert 2-site consistency group. Alternatively, you can select Actions > Convert to 3-site from detailed view for the selected 2-site consistency group.
Select either the new or existing 2-site consistency group that contains relationships and select Next. If a new consistency group does not display, select Refresh.
For Group page, enter the following settings:
Cycle period

Enter the number of seconds between replication cycles between the asynchronous source and the auxiliary-far system.

Select the site for asynchronous source
Select one of the two configuration models displayed.
- Select Cascade if you want asynchronous copy between the systems at the auxiliary-near site and the auxiliary-far site. In this configuration, the auxiliary-near site is the source of the asynchronous copy to the auxiliary-far site. The full topology looks like this:
  Figure 1. Cascade topology
- Select Star if you want asynchronous copy between the systems at the master site and the auxiliary-far site. In this configuration, the system at the master site is the source of the asynchronous copy to the auxiliary-far site. The full topology looks like this:
  Figure 2. Partnership between master site and auxiliary-far site
Click Next.
Under Choose a pool, specify the numerical ID for the storage pool on the auxiliary-far site that provides capacity for the target volumes. To verify these details, select Launch the Aux-Far management GUI, and select Pools > Pools. If the selected pool is a data reduction pool, select This is a data reduction pool.
Under Aux-Far pool settings, select the method for saving capacity that this pool uses.
In the Volume base name field, enter a naming convention that identifies the volume as part of the 3-site consistency group. The names are automatically generated to include the specified base name, the name of the 3-site consistency group, and an incremental number.
Click Convert.
After the conversion completes, verify that the Metro Mirror relationship is part of the 3-site consistency group. Select the 3-site consistency group and verify that all its relationships display in the list of relationships.
If the conversion does not complete fully, the 3-site consistency group displays the Partial state (). If that occurs, select the 3-site consistency group and select Actions > Resume conversion to 3-site.

Using the command-line interface

To add a independent relationship to an existing 3-site consistency group, complete the following steps:

Run the lsrcconsistgrp command on the storage system to verify the state of the consistency group.

The command must specify the consistency group.

[09:15:08] Master-SVC-Node:~ # lsrcconsistgrp CG0
id 0
name CG0
master_cluster_id 0000010030807F4A
master_cluster_name Master
aux_cluster_id 0000010027007DA0
aux_cluster_name AuxNear
primary master
state consistent_synchronized
relationship_count 3
freeze_time 
status 
sync 
copy_type metro
cycling_mode 
cycle_period_seconds
previous_primary 
channel none
RC_rel_id 0
RC_rel_name rel0
RC_rel_id 1
RC_rel_name rel1
RC_rel_id 2
RC_rel_name rel2

Run the convertrcrelationship command to convert the first 2-site relationship to a 3-site relationship.
```
[root@ORCH-HOST cli]# $convertrcrelationship  -type 3site  -cycleperiod 300 -periodicsrc Master -pool 0 -iogrp 0 rel0
```
The -periodicsrc parameter specifies the site that is responsible for replicating data to the auxiliary-far site.

Specify volume parameters the same as the attributes of volumes between Metro Mirror relationships. For example, compressed and thin-provisioned. In this example, -pool on the auxiliary-far site where the new volume is expected to be created is 0, and -iogrp is 0.
Run the convertrcrelationship command to convert the remaining relationships to 3-site relationships.
```
[root@ORCH-HOST cli]# convertrcrelationship  -type 3site -pool 0 -iogrp 0 rel1
[root@ORCH-HOST cli]# convertrcrelationship  -type 3site -pool 0 -iogrp 0 rel2
```
The remaining relationships in the source consistency group can be converted without specifying the -cycleperiod and -periodicsrc parameters.

Data cycling is automatically started after all relationships in the source consistency group are converted in the 3-site consistency group.

[root@ORCH-HOST cli]# ls3sitercconsistgrp
name state              primary periodic_copy_source sync_copy_state          periodic_copy_state freeze_time cycle_period status
CG0  3site_inconsistent AuxNear Master               consistent_synchronized  copying                         300          online

Run the ls3sitercrelationship command to verify the state of the 3-site relationships.

[root@ORCH-HOST cli]# ls3sitercrelationship
name  consistgrp master_vdisk_id auxnear_vdisk_id auxfar_vdisk_id sync_copy_progress periodic_copy_progress status  
rel0  CG0        0               0                11                                 Master                 complete
rel1  CG0        1               1                14                                 Master                 complete
rel2  CG0        2               3                18                                 Master                 complete