[ceph-users] Why a lot of pgs are degraded after host(+osd) restarted?

Hi all, While I am testing host failover, there are a lot of degraded pg after host(+osd) is up. In spite that it takes a short time to restart, I don't understand why pg should check all objects related to the failed host(+osd). I'd like to know how to prevent to become degraded pg when osd restart. FYI. degraded pg means "active+undersized+degraded+remapped+backfilling" pg state