These systems support zero-downtime snapshots. You tell it to snapshot, it instantly snapshots, you can run a differential/incremental backup at great speeds. Your RAID controller is already caching the hot data, so the impact is minimal.

Except network cost there's no extra disk required. It's just broadcasted writes consumed on the other hand.

These boxes are not dumb JBODS. They support their own replication/backup subsystems, so everything is transparent.