Clearer understanding for glusterfs for replication

OK, looks like this is the actual question:

At which time does file01 which is generated on server01 appears on server02, when does replication takes place?

The replication starts as soon as the file is created/changed/deleted on server01. Exactly how long replication takes to complete depends on the storage I/O, network bandwidth and how much data needs to be replicated.

The way I've used glusterfs, the files that live in the gluster volume are usually small so replicating a new file is almost instantaneous.

Update: As for whether you should write directly to the brick (/var/appdata) or the mount (/var/gfs_appdata), the way I understand it, you should always use the mount to read and write. Honestly, I don't know the details of exactly why this is the case, a (now ex-) colleague did a lot of testing with glusterfs about a year ago before we started using it and I haven't acquainted myself with the finer details.

Here's an answer on a similar question which gives a bit of detail explaining why it should be done that way: Can Apache Read The GlusterFS Brick Directly But Write To The GlusterFS Mount?