OSF DCE Administration Guide--Introduction

OSF DCE Administration Guide—Introduction

If information changes frequently and users in your network depend on the

accuracy of that information, you need to consider how much you rely on

replication. It is better to go to a central source of information for data that

changes frequently. If users look up information but do not need to change the

information that is shared with other users, you can rely more on replicated

data.

• Is the most important data the most available data? Have you made plans to

replicate this data?

CDS, GDS, the Security Service, and DFS maintain master copies of their

respective databases. Each CDS directory can be replicated separately. In

addition to DFS databases, individual DFS ﬁlesets or groups of ﬁlesets can be

replicated. GDS replication, also known as shadowing, can be done for a single

object or an object and its subordinates (a subtree). The Security Service

replicates the entire registry database. Because other components depend on the

information managed by the Security Service and parts of the CDS namespace,

that data needs to be available at all times. For example, the special character

string /.: (the cell root) is stored in CDS and must always be available.

Keep in mind that while replicating data improves availability, there is a cost in

terms of performance and the amount of administration required.

• If your network has a gateway, are the servers located on the same side of the

gateway as the clients that rely on those servers?

CDS servers broadcast messages at regular intervals to advertise their existence to

CDS clerks in the network. Clerks learn about servers by listening for these

advertisements. Placing the servers and the clients that rely on them on the same side

of the gateway facilitates efﬁcient updates of information and a quick response to

client requests. Additional administration is required if you rely on servers that are

not available through the advertisement protocol, which is effective only in a local

area network.

Consider how fast and how expensive links are if you are administering a cell that

includes users in different geographic locations. You may want to keep more

information locally to reduce your dependence on transmitting information across

links.

• Is communication limited to your own cell, or do you need to communicate with

other cells?

DCE offers two methods of connecting cells so that they can communicate:

— The standard intercell connection, in which a cell is registered in a global

directory service that DCE supports and communicates with other cells registered

in that directory service. A cell can be registered in both the GDS and DNS

directory services. In this case, the cell has two names: one in GDS format, and

one in DNS format. These names are the cell’s ‘‘aliases’’.

— The hierarchical cell connection, in which a cell is registered in another cell’s

CDS namespace, and communicates with other cells also registered in that cell’s

namespace. In a hierarchical cell conﬁguration, the cell at the top of the

hierarchy must be registered with a global directory service, but the cells beneath

it do not need to be, because they communicate through CDS.

2− 2 Tandem Computers Incorporated 124244