Mostly from the SnapRaid manual.
With SnapRaid the data on the drives need to have parity information calculated and stored on a regular basis.
# snapraid sync
It's probably best to do this nightly (or weekly if your data doesn't change much).
zackreed.me has a tutorial and custom script which will largely automate running of sync and verifying data.
Scrubbing the pool periodically will look for data and/or parity errors. It verifies the data in the pool with the hash which was computed via the sync command.
# snapraid scrub
As it scrubs any errors will be listable via the status command.
# snapraid status
To have snapraid try to fix the errors:
# snapraid -e fix
Confirming the fix succeeded:
# snapraid -p bad scrub