PowerStore: Asynchronous replication session may re-sync the delta data after PowerStore NDU (Non Disruptive Upgrade)

If a user did not manually pause a syncing replication session before performing a Non-Disruptive Upgrade (NDU), they may find that the 'Replication Remaining Data' has increased after the session is resumed following the completion of the NDU.

If a replication is not paused, the PowerStore system will automatically put it in a "System_Paused" status during the Non-Disruptive Upgrade (NDU) and resume it after the NDU is completed. However, when the replication session is in a syncing status, a code issue may cause the system to incorrectly remove the Recovery Point Objective (RPO) snapshot during the "System_Paused" stage. As a result, when the replication is resumed, a new RPO snapshot will be created without the previous synced data record, effectively restarting the replication from address 0.

A user may encounter this issue when all of the following three conditions are met simultaneously: 

1. Async replication is in a syncing status
2. An NDU is ongoing
3. The code bug is triggered during System_Paused stage

The issue has been resolved in PowerStore OE code version 4.4 and later. For OE versions prior to 4.4, users can work around this issue by manually pausing any syncing replication sessions before performing an NDU.