4 GB raspberry pis are especially prone to crashes. disabling fast-sync helps but i still saw crashes. as somerfeld recommends, during initial sync i did nightly backups of db so i didnt have to start from scratch on crash. in my case, cause of crash was bitcoind connection error; may have sthg to do with communication with ssd. in any event, what i ended up doing was monitor fulcrum log and stop fulcrum for maybe an hour or so whenever i started seeing bitcoind connection errors.