We just moved to PG9.6 from 9.1 (yeah, not my choice to wait this long). In 9.1 I had to make the archive location (NFS in my case) available to all the mirrors running PG so that they could catch up whenever they fell behind. I thought I read somewhere that in 9.6, as long as the WAL log is available on disk or in the archive the replication server will provide that to the replication client, and my archive NFS mount didn’t have to be available to all replication clients. It doesn’t seem to be operating that way though. Did I completely remember that wrong or did I misunderstand something?
The master won't read from the archives for you in order to send to an replica. But using replication slots, you can keep the needed log files right in pg_xlog/pg_wal until all replicas get what they need (assuming the disk is large enough). Then you don't need an archive at all for replication purposes, still might for pitr purposes.
