Currently, I'm running once a week manually nodetool repair (while no action is happening to the cassandra nodes (nothing is inserted, e.t.c.)). Just wondering, if I can run nodetool repair, while data is being inserted?
Secondly - Can I create a script in crontab, that automatically runs every week nodetool repair, and is ocne a week enough to run nodetool repair?
yes, if running one repair at a time you shouldn't be impacting normal usage. Instead of a cron job i would recommend using reaper (free and open source) for automating it. Would give you a bit more visibility and it handles things a bit better than just the default that running from nodetool provides.