At UT/ORNL, the Netlib repository contents are replicated on two machines. The master copy resides on netlib2.cs.utk.edu, while the slave copy resides on netlib1.epm.ornl.gov. Both machines are registered with the Domain Name System as host addresses for the domain name netlib.org. Theoretically, the load balance for Xnetlib requests between the two machines should be about 50/50. The mail preference is currently set up so that netlib1 gets most all of the email requests. If netlib1 is down, however, email requests should get sent to netlib2.
Updates to the repository must be made on the master copy on netlib2. When a staff person makes an update, either by installing a new library or by changing or adding files in an existing library, that person is supposed to run a script that logs the change and asks him or her whether to propagate the change to netlib1. When the person answers yes, the update is propagated by running the rdist command. A nightly cron job runs an rdist job using a distfile that lists all the libraries that are replicated. The rdist job checks for discrepancies, propagates any changes, and notifies the Netlib maintenance staff of any such changes.
At AT&T, the email server runs on one machine (inside the security firewall) where the editorial staff can conveniently maintain the file tree. A second machine (outside the firewall) replicates the files, in compressed form, for ftp service. The latter machine runs the Plan9 operating system, which provides a file system that allows one to see the state as of any date in the past.