Dfs-R As Backup; Dfs-R And Simultaneous File Sharing - LaCie 12big Rack Network Technical Brief

LaCie Professional Server DFS-N & DFS-R
Technical Brief: DFS
page 14

3.2.2. DFS-R as Backup

While the primary goal of our example is to improve bandwidth
performance, there are other advantages to employing DFS replica-
tion. As it turns out, replicating data to other servers is a simple and
effective way to configure an automatic backup.
As seen in Table 04 - Replicating Folders, folders are replicated
across three servers. In the event that one of the servers requires
temporary servicing or must be updated, the data will still be avail-
able to users due to replication on the other two servers. Further, it
is relatively transparent since the DFS-R knows to go to an available
server for the requested file(s).

3.2.3. DFS-R and Simultaneous File Sharing

While DFS-R is perfect for providing local (LAN) access to files
stored on remote servers (WAN), users are cautioned when sharing
or working on a document within the same period of time. DFS-R
does not look to a "master" server that sets the rules on how a file
is replicated. Rather, it is more democratic, intuitively updating rep-
licated files in all locations, no matter where the changes occur. If
a file is opened on one workstation at LaCie New York and another
workstation at LaCie Paris at the same time, DFS-R will replicate the
changes from the last user who chooses Save ("last writer wins").
Edits registered just before the last user will go into a folder called
"Conflict and Deleted" on one of the servers. Access to the Conflict
and Deleted folder is limited to members of the local Administrators
group.
On a LAN, a user receives a warning if a file is in use. DFS-R, how-
ever, does not search the WAN for replicated versions when a file is
opened. This means that users at LaCie Paris and LaCie New York
can work on the same accounting spreadsheet at the same time.
If LaCie Paris logs his changes at 11:02 EST and LaCie New York
saves her version at 11:03 EST, the New York version is used by the
RDC for replication. The Paris version goes into the Conflict and
Deleted folder.
A second potential conflict could arrive when users are not working
on a document at the same time but within a period between file
replications. For example, the user at LaCie Paris edits a file and
saves it. Soon after, the user at LaCie New York opens the same
file, makes changes, and saves. Since there was no replication dur-
ing the interval that LaCie Paris and LaCie New York saved their
respective files, only the changes made by LaCie New York will be
replicated. The changes made by LaCie Paris will be ignored and his
file stored in the Conflict and Deleted folder.
An administrator should consider how often files must be simultane-
ously accessed or revised in a limited period of time. If users will
work on replicated files at the same time, there are third-party soft-
ware solutions for DFS-R to integrate file locking over a WAN.