Using Replication For High Availability - Netscape DIRECTORY SERVER 6.1 - DEPLOYMENT Deployment Manual

In addition, as there is a single change log on every supplier server, if a
supplier contains multiple replicated databases the change log will be used
more frequently, and the disk usage will be even higher.
• Server threads—Each replication agreement consumes one server thread. So,
the number of threads available to client applications is reduced, possibly
affecting the server performance for the client applications.
• File descriptors—The number of file descriptors available to the server is
reduced by the change log (one file descriptor) and each replication agreement
(one file descriptor per agreement).

Using Replication for High Availability

Use replication to prevent the loss of a single server from causing your directory to
become unavailable. At a minimum you should replicate the local directory tree to
at least one backup server.
Some directory architects argue that you should replicate three times per physical
location for maximum data reliability. How much you use replication for fault
tolerance is up to you, but you should base this decision on the quality of the
hardware and networks used by your directory. Unreliable hardware needs more
backup servers.
NOTE You should not use replication as a replacement for a regular data
backup policy. For information on backing up your directory data,
refer to the Netscape Directory Server Administrator's Guide.
If you need to guarantee write-failover for all you directory clients, you should use
a multi-master replication scenario. If read-failover is sufficient, you can use
single-master replication.
LDAP client applications can usually be configured to search only one LDAP
server. That is, unless you have written a custom client application to rotate
through LDAP servers located at different DNS hostnames, you can only configure
your LDAP client application to look at a single DNS hostname for a Directory
Server. Therefore, you will probably need to use either DNS round robins or
network sorts to provide fail-over to your backup Directory Servers. For
information on setting up and using DNS round robins or network sorts, see your
DNS documentation.
Defining a Replication Strategy
Chapter 6 Designing the Replication Process 119