Here are some of the requirements to enable flash backups,
1. OS/400 V5R3 or higher.
2. Both the production and backup system i partitions/system require the HA switchable resource option of OS/400(Option 41)
3. Each system/partition will require its own fiber channel attachment cards.
4. Copy services flash copy or metro/Global mirror or both are enabled on IBM system storage.
Here are few links which gives some more details: