diff --git a/backfiller/backfiller/main.py b/backfiller/backfiller/main.py
index 7ef630b..9a27a03 100644
--- a/backfiller/backfiller/main.py
+++ b/backfiller/backfiller/main.py
@@ -195,7 +195,7 @@ class BackfillerManager(object):
 	NODE_INTERVAL = 300 #seconds between updating list of nodes
 
 	def __init__(self, base_dir, channel, qualities, static_nodes=[],
-			start=None, delete_before=0, run_once=False, node_file=None,
+			start=None, keep_hours=0, run_once=False, node_file=None,
 			node_database=None, localhost=None, download_concurrency=5,
 			recent_cutoff=120):
 		"""Constructor for BackfillerManager.
@@ -206,7 +206,7 @@ class BackfillerManager(object):
 		self.qualities = qualities
 		self.static_nodes = static_nodes
 		self.start = start
-		self.delete_before = delete_before
+		self.keep_hours = keep_hours
 		self.run_once = run_once
 		self.node_file = node_file
 		self.db_manager = None if node_database is None else database.DBManager(dsn=node_database)
@@ -240,14 +240,14 @@ class BackfillerManager(object):
 		self.workers.pop(node).stop()
 
 	def delete(self):
-		"""Delete old hours."""
+		"""Delete hours older than self.keep_hours ago."""
 
-		self.logger.info('Deleting hours older than {} hours ago'.format(self.delete_before))
+		self.logger.info('Deleting hours older than {} hours ago'.format(self.keep_hours))
 
 		for quality in self.qualities:
 			hours = list_local_hours(self.base_dir, self.channel, quality)
 			
-			cutoff = datetime.datetime.utcnow() - datetime.timedelta(hours=self.delete_before)
+			cutoff = datetime.datetime.utcnow() - datetime.timedelta(hours=self.keep_hours)
 			hours = [hour for hour in hours if hour < cutoff]
 
 			for hour in hours:
@@ -477,7 +477,7 @@ class BackfillerWorker(object):
 @argh.arg('--static-nodes', help='Nodes to always backfill from. Comma seperated if multiple. By default empty.')
 @argh.arg('--backdoor-port', help='Port for gevent.backdoor access. By default disabled.')
 @argh.arg('--start', help='If a datetime only backfill hours after that datetime. If a number, bacfill hours more recent than that number of hours ago. If None (default), all hours are backfilled.')
-@argh.arg('--delete-before', help='Delete hours older than this number of hours ago. If 0 (default) do not delete any hours.')
+@argh.arg('--keep-hours', help='Only keep this number of hours. If 0 (default) keep all hours.')
 @argh.arg('--run-once', help='If True, backfill only once. By default False.')
 @argh.arg('--node-file', help="Name of file listing nodes to backfill from. One node per line in the form NAME URI with whitespace only lines or lines starting with '#' ignored. If None (default) do not get nodes from a file.")
 @argh.arg('--node-database', help='Postgres conection string for database to fetch a list of nodes from. Either a space-separated list of key=value pairs, or a URI like: postgresql://USER:PASSWORD@HOST/DBNAME?KEY=VALUE . If None (default) do not get nodes from database.')
@@ -485,7 +485,7 @@ class BackfillerWorker(object):
 @argh.arg('--download-concurrency', help='Max number of concurrent segment downloads from a single node. Increasing this number may increase throughput but too high a value can overload the server or cause timeouts.')
 @argh.arg('--recent-cutoff', help='Minimum age for a segment before we will backfill it, to prevent us backfilling segments we could have just downloaded ourselves instead. Expressed as number of seconds.')
 def main(channels, base_dir='.', qualities='source', metrics_port=8002,
-	static_nodes='', backdoor_port=0, start=None, delete_before=0,
+	static_nodes='', backdoor_port=0, start=None, keep_hours=0,
 	run_once=False, node_file=None, node_database=None,
 	localhost=socket.gethostname(), download_concurrency=5, recent_cutoff=120):
 	"""Backfiller service."""
@@ -499,13 +499,13 @@ def main(channels, base_dir='.', qualities='source', metrics_port=8002,
 		try:
 			start = float(start)
 			logging.info('Backfilling last {} hours'.format(start))
-			if delete_before and start > delete_before:
-				logging.warn('Keeping fewer hours ({}) than backfilling ({})'.format(delete_before, start))
+			if keep_hours and start > keep_hours:
+				logging.warn('Keeping fewer hours ({}) than backfilling ({})'.format(keep_hours, start))
 		except ValueError:
 			start = dateutil.parse(start)
 			logging.info('Backfilling since {}'.format(start))
-			if delete_before:
-				logging.warn('Only keeping {} hours when backfilling since {}'.format(delete_before, start))
+			if keep_hours:
+				logging.warn('Only keeping {} hours when backfilling since {}'.format(keep_hours, start))
 
 	common.PromLogCountsHandler.install()
 	common.install_stacksampler()
@@ -516,7 +516,7 @@ def main(channels, base_dir='.', qualities='source', metrics_port=8002,
 	for channel in channels:
 		logging.info('Starting backfilling {} with {} as qualities to {}'.format(channel, ', '.join(qualities), base_dir))
 		manager = BackfillerManager(base_dir, channel, qualities, static_nodes,
-				start, delete_before, run_once, node_file, node_database,
+				start, keep_hours, run_once, node_file, node_database,
 				localhost, download_concurrency, recent_cutoff)
 		managers.append(manager)
 		workers.append(gevent.spawn(manager.run))