FileReplicationPro judges a file change event by two indicators and to do that it uses two mechanisms.
File Change detection:
1. The time date modified is updated to a newer date than exists on the other machine.
2. The ACL has been updated.
Mechanisms:
1. If the job is real-time, an OS hook monitors the disk for either of the above items, the file modified date stamp or ACL change. These are passed directly into a real time job for immediate execution. You should be aware that a NAS unit is unable to detect and report real time changes that occur on the device to FRP. A NAS has it's own self contained OS and since FRP cannot be resident on the NAS, real time is not an option for change detection on the NAS. Real time detection for certain OSes such as Netware, AIX, and older versions of Linux which do not provide Inotify or Jnotify are not supported 1.
2. If the job is repeating job on a schedule or once every 24 hours if a real time job. ( 24 hours is the default cleanup pass in real time jobs 2). FRP performs a dir-walk of the folders on both machines in the job. It compares for modified date stamp or ACL change replicating any newer items found.
Notes:
1 Some administrators with OSes such as Netware, Aix, Sun, NAS devices, or machines that do not support real time may want to use the Real Time Alternative Setting.
2 The real time default clean-up pass is a dir-walk job that is designed to execute automatically and is spawned according to the interval set in the /etc/s2s.properties file. The default value is s2s.realtime.dir_walk_interval=720 the value is in minutes. The purpose of this feature is to detect and replicate any events missed by the real time job that spawned it. Events that can cause the loss of real time events are rare, but the reporting of events in real time is sometimes not perfect in a very busy OS, or some environmental event such as a power surge or hardware issues can cause the OS to not report in real time.
Please take note that providing the above information about the s2s.properties file is not an invitation to change this or other settings found there. An incorrect setting for values in this file can lead to massive data loss or extremely unpredictable performance.