fix bug in replica_stub::on_disk_stat && improve logging
fix bug in replica_stub::on_disk_stat && improve logging

Summary: Ref T10570

Test Plan: N/A

Reviewers: sunweijie, cailiuyang

Reviewed By: sunweijie

Subscribers: #pegasus

Maniphest Tasks: T10570

Differential Revision: https://phabricator.d.xiaomi.net/D84069

shengofsun/rDSN,shengofsun/rDSN,shengofsun/rDSN,shengofsun/rDSN,shengofsun/rDSN,shengofsun/rDSN,shengofsun/rDSN,shengofsun/rDSN