When an SI pair contains a DP-VOL that is larger than 4,194,304 MB (8,589,934,592 blocks), the differential data is managed by the pool to which the pair is related. If differential data management fails due to insufficient pool capacity, you need to release the differential data (pages) managed in the pool. You also need to release pages when you downgrade to a microcode version that does not support SI pairs with volumes larger than 4,194,304 MB.