| We are all familiar with the Novell recommendation of having at least three replicas for a given partition for the sake of fault tolerance. This is relatively easy to implement in mid- and large- size installations where there are multiple servers. However, how can you provide a similar level of fault tolerance to single-server sites? In the past, the solution has been to install a low-end NetWare server and put a two- user or a runtime license on it. This provides the customer with two replicas, which is better than having just one. However, there are two major drawbacks. One is that the customer will have to purchase a second server license. The other is the added administrative overhead resulting from the users attaching to this second server and not getting the correct drive mappings, for instance. With the introduction of eDirectory, which runs on multiple operating system platforms, we have a couple more options to choose from. Although not officially supported nor endorsed by Novell, one could easily install eDirectory on a Windows NT 4.0 Workstation machine (with Service Pack 3 or higher) and use it to host a second copy of the replica. Windows NT workstations are relatively easy to come by, and the hardware requirement is generally lower than that of a NetWare server. On the other hand, with the popularity and availability of freely downloadable Linux today, you can use a SuSE or Red Hat Linux system to host additional replicas. The drawback here is that you need to learn some Linux if you don't already know it. The benefit is that you don't need to pay for the operating system, and the associated hardware costs less than a standard Windows system. TIP If you have remote sites that have single servers at those locations, you can consider using a Windows or Linux system to host a second replica at each of those remote sites. In case the main server is unavailable, the users can still authenticate to eDirectory and access other DS -based services without having to cross the WAN.
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