For https://phabricator.wikimedia.org/T108850 we'd need to apply the eventlogging_cleaner.py purging strategy to db1107 (m4-master) to be fully compliant with data retention policies. We don't expect any big issue since we triple checked data consistency on db1108 (that is already running the purging strategy) but a bit of paranoia whispered in my ears that a backup before proceeding would surely be better (for example, say we discover a weird purging bug two weeks from now, it would be nice to have a way to recover data if needed).

Two options are available:

1. binary backup, in which we 1) stop mysql 2) copy data from /srv/sqldata to /srv/backup 3) start mysql. This is surely faster but it has one caveat: once mysql on db1107 goes down, m4-master will failover to db1108. We could stop mysql insertion from eventlog1001 so it shouldn't be a big problem.

2. logical backup, using mydumper to /srv/backup, that would not require to stop mysql but it may take hours to complete.

I am fine with both options, maybe 1) seems the quickest and less painful for everybody. We'd need to complete this work early this week if possible, to start purging data and apply the eventlogging_cleaner.py's cron script permanently.

Thanks in advance!