Data Protection for a backup job is set as 2 weeks. However last week's data protection under Internal database in HP DP shows as 1 week 18 hrs. Is it reducing the period or something under 2 weeks. PFA
your screen shot is not from the Internal Database View but from a certain medium under Devices & Media. In this view, DP displays exactly the remaining protection for the given objects on the given medium, so you can see when they expire and which object may keep a certain medium from expiring. So that view is correct provided you looked into a medium that was written approximately a week before taking this screen shot.
As to an object with Permanent protection suddenly going None or Expired, that shouldn't happen without manual interaction (explicitely recycling the medium or at least unprotecting the given object).
max retention setup for backups is 3 weeks. then is it still ok to setup IDB retention as permanent ?
That's your decision (depends on a lot of factors, including local policies). If it were mine, I'd ponder:
If my data retention is 3 weeks, do I really need the ability to restore an IDB that is way older? Even with longer data protection on backups, what use is an outdated IDB? If you ever have to recover the IDB, it's probably the newest (disaster struck) or the one from a day or two before (the IDB got corrupted and you want to backtrack to last known good).
If the IDB backup is mixed with the other backups on the same media, having it protected significantly longer than that data is a very bad idea. It will block these media from expiring (potentially forever). You have to make sure it goes to dedicated media then, ideally via a dedicated pool.
Personally, I don't see any sense in a long term protection of IDB backups, let alone the default of Permanent. You may occasionally archive an IDB backup to archive media just to sleep better, but the value quickly decreases with age and a year-old IDB would only allow you to recover a CM that has so many additional changes to be applied that rebuilding it from scratch might be simpler. Of course, that all depends on your cell dynamics and starting from such old IDB may still be a crucial time saver. In the end, for your installation, nobody can tell better than yourself.