Upgrades of i5/OS® releases made to any nodes involved in geographic mirroring require a rolling upgrade. The system will perform geographic mirroring from a V5R3M0 node owning the production copy to a V5R4M0 node owning the mirror copy. A rolling upgrade is required because a node at an earlier release might not be able to perform geographic mirroring to a node at a later release and a node at a later release usually cannot perform geographic mirroring to a node at an earlier release. This forces the nodes to be upgraded in an order dictated by the recovery domain order starting with the node that is the last backup. During the rolling upgrade, the production copy and mirroring copy will be moved to their recovery nodes.
In the following example, four nodes at two sites supporting mutual takeover will be upgraded. Nodes A and B are on one site with nodes C and D at another site. Node A owns the production copy of independent disk pool 33, and node C owns the mirror copy of independent disk pool 33. Node C owns the production copy of independent disk pool 34, and node A owns the mirror copy of disk pool 34.
| Steps | Recovery domain order | |||
|---|---|---|---|---|
| Independent disk pool 33 | Independent disk pool 34 | |||
| During | After | During | After | |
| Initial | A, B, C, D | C, D, A, B | ||
| 1. Upgrade node D | A, B, C | A, B, C, D | C, A, B | C, A, B, D |
| 2. Upgrade node B | A, C, D | A, C, B, D | C, A, D | C, A, D, B |
| 3. Switch production copy of independent ASP 34 (C to D) | D | |||
| 4. Switch mirror copy of independent ASP 34 (A to B) | D, B | |||
| 5. Switch mirror copy of independent ASP 33 (C to D) | A, B, D | |||
| 6. Upgrade node C | A, B, D | A, B, D, C | D, B | D, C, B |
| 7. Switch mirror copy of independent ASP 33 (D to C) | A, B, C, D | D, C, B | ||
| 8. Switch prod copy of independent ASP 34 (D to C) | A, B, C, D | C, D, B | ||
| 9. Switch production copy of independent ASP 33 (A to B) | B, C, D | C, D, B | ||
| 10. Upgrade node A | B, C, D | B, A, C, D | C, D, B | C, D, B, A |
| 11. Switch production copy of independent ASP 33 (B to A) | A, B, C, D | C, D, B, A | ||
| 12. Switch mirror copy of independent ASP 34 (B to A) | A, B, C, D | C, D, A, B | ||
In step 3 of the table, notice that node A cannot mirror node D because node D is release n+1 while node A is still at release n. Therefore, the mirror copy for Independent ASP 34 is switched to node B which is now at release n+1. Steps 7, 11, and 12 (new numbers after added steps) are not strictly required and can be done later or omitted. They were done here to return the roles to their preferred owners.