Configuring an active-active relationship from an existing two-copy volume

You can configure an active-active relationship from an existing two-copy volume.

Before you begin

This task is used to convert from a stretched system to a HyperSwap® topology system. Stretched volumes on SAN Volume Controller can be converted to active-active relationships by splitting the stretched volume copies and then making an active-active relationship between them. You can complete this task without disrupting host applications and without impacting the high availability of the volumes.

About this task

This task assumes that the existing stretched system has the following configuration:

Site A has node siteAnode1 in I/O group 0, siteAnode2 in I/O group 1, and mdiskgrp 0 local
Site B has node siteBnode1 in I/O group 0, siteBnode2 in I/O group 1, and mdiskgrp 1 local

The existing two-copy volume was created with a command such as the following example:

mkvdisk -size 1 -unit tb -iogrp 0 -mdiskgrp 0:1 -copies 2 -name stretchedVol0

The system might be in stretched topology if the requirements were satisfied and the topology was set:

chsystem -topology stretched

The hosts with stretched volumes all need to have extra volume access. Make sure that this access is possible, which requires that you check how many volumes a host has mapped in each I/O group.

To configure active-active relationship from existing stretched volumes, complete the following steps:

Procedure

Update to 7.5 or later software so that active-active relationships are supported and topology can be set to hyperswap.
Move out of stretched topology if needed, so that the nodes can be reconfigured. For example, look for the topology value in the output from the lssystem command. Change the topology:
```
chsystem -topology standard
```
Logically move nodes so both nodes in an I/O group have matching sites. No physical move is needed. You must reassign the WWPNs from one node to another node to make sure that the WWPNs stay in the same I/O group. (So they move site and the host maintains access to a certain volume through a certain WWPN.) For example:
```
rmnode siteAnode2
rmnode siteBnode1
```
Use the service assistant interface or the front panel display and buttons if available to change the WWNN of siteAnode2 and siteBnode1.
```
addnode -panelname siteAnode2 -wwnodename WWNN iogrp 0 -name siteAnode2 -site 1
addnode -panelname siteBnode1 -wwnodename WWNN -iogrp 0 -name siteBnode1 -site 2
```
Now that both nodes in an I/O group are at the same site, change the topology to hyperswap.
```
chsystem -topology hyperswap
```
Split the stretched volume and make the active-active relationship between the master volume and the auxiliary one.
```
splitvdiskcopy -copy 2 -iogrp 1 -name stretchedAux0 -activeactive
```
After creation, the relationship is inconsistent_stopped. If the -sync parameter was provided, the relationship is consistent_stopped.

Rename the relationship for future use.

chrcrelationship -name activeRel0 relationship_id

Relationships can be added to consistency groups.
- Create a consistency group: mkrcconsistgrp -name consistgrp0 (note that empty groups have no type)
- Add an active-active relationship: chrcrelationship -consistgrp consistgrp0 activeRel0
Active-active relationships must have a master and an auxiliary change volume that is defined by using the following commands:
```
mkvdisk -iogrp 0 -mdiskgrp siteAmdiskgrp -size 1 -unit tb
 -rsize 0 -name mastcv0 
mkvdisk -iogrp 1 -mdiskgrp siteAmdiskgrp -size 1 -unit tb
 -rsize 0 -name auxCV0 
```
```
chrcrelationship -masterchange mastCV0 activeRel0
chrcrelationship -auxchange     auxCV0 activeRel0
```
When a relationship has both change volumes that are defined, it starts synchronizing. If the relationship is in a consistency group, only the synchronization process completes. When all relationships in the group copy their data, the relationship changes to the consistent_synchronized state.
Add access to the master volume via I/O group 1:
```
addvdiskaccess -iogrp 1 stretchedVo10
```
For any remaining stretched volumes that you want to convert, repeat starting at step 5.