“А шо эта ваш бэкап такой уставший?”*

RHA replicates at File system level. This allows to replicate individual files and folders (not whole device as you would with DRBD) — over the WAN this translates into significant savings of time/traffic (also at block level you typically see more updates/writes so you would replicate more data with DRBD)
Besides that, RHA includes tones of useful features ( supports different replication modes, different restore options, different destinations, has applications intelligence, cross platform… List is long… ). Long story short — RHA is a Swiss army knife :)