Postgresql, write archive file over mount, secure against simultaneous access?
Neither NFS nor cp will protect you from partial write. The usual way of mitigating problems with write atomicity is to use a temporary file and a mv after copying (or writing) is complete.  You might use something like:

    test ! -f /mnt/server/archivedir/%f &amp;&amp; cp %p /mnt/server/archivedir/tmp/%f &amp;&amp; \
    mv /mnt/server/archivedir/tmp/%f /mnt/server/archivedir/%f