Working with Spool Servers

In this lesson, you will learn about the concept of logical spool servers (or – for short – logical servers) and how to set them up.

In the SAP printing concept, an output device is assigned to just one spool server. A spool server, on the other hand, can have multiple output devices assigned to it, which raises the risk of this server becoming overloaded. You should, therefore, have a mechanism for load balancing across multiple servers. Having groups of spool servers is also recommended for reliability reasons. Both of these aspects are taken into account in the implementation of logical spool servers, also called logical servers.

A logical server stands for one or more other logical and/or real SAP spool servers. Logical servers can be used in place of real SAP spool servers anywhere in the spool system. The logical server is a placeholder for the spool server assigned to it, while a real server is an actual application server with a spool work process and can output print requests.

The figure Logical Servers: Concept illustrates a basic scenario involving logical servers. A (real) spool server is an SAP application server with at least one spool work process. Every output request is processed on a real spool server of this type. An output device created in the SAP system can be assigned to a real spool server directly. However, there are many advantages associated with an additional logical layer between the output device and the spool server. You can use logical (spool) servers for this purpose. These stand for a hierarchy of other logical servers and/or real spool servers.

You manage spool servers in transaction SPAD, on the Devices / servers tab in the Spool Servers area. The following terminology is relevant when setting up a spool server (see figure "Creating a Logical Server"):

Server name (field AS Instance)

The name of the spool server can have a maximum of 20 characters and is case-sensitive. You can use an additional field a short description.

Server class

You can classify the spool server here (for high-volume printing, for example).

Logical server

Select this field when you create a logical server.

Allow load balancing

You use this field to control which method the system uses to determine a spool server for processing of output requests. When the field is set, the system searches for the server with the lowest load among the hierarchy of logical and/or alternative servers you have defined (valid both for logical and physical spool servers).

Mapping

The name of a real or logical server to which this logical server refers.

Alternative server

The server that should be used if the current server is down or not available.

You can use dynamic server selection without restrictions only for output devices that are defined with remote access methods S and U or with the local OMS access method E. The reason for this is that the SAP system accesses remote printers using a network link. This network link is likely to be usable without adjustment by any spool server. Output requests for a remote printer can therefore be moved from one spool server to another without causing any problems. Output Management System (OMS) printers are accessed by a print command that can be executed locally from any spool server. Requests for OMS printers can therefore also be moved from spool server to spool server without problems.

For local printers (access methods C and L), on the other hand, dynamic server selection requires some preparation at the operating system level. In a local connection, the SAP spool server passes an output request directly to the spooler or print manager in the host on which it is running. Such an output request can be processed at another server only if the local spooler or print manager at the second spool server can identify the target output device. This means that the target output device must be defined under the same name in both local spoolers (in the host of the first spool server, and also in the second host). Otherwise, switching an output request for such a device to another spool server could generate the error Device unknown from the local spooler or print manager.

You can classify spool servers according to their intended use, such as a spool server for mass printing or for production printing. This classification helps to make your print architecture clearer. It also helps you to realize your planned print architecture, such as assigning classified output devices to the correct spool server.

You can classify output devices and spool servers, for example, for test printing or production printing. To classify an output device, select it (in transaction SPAD under Output Devices) and choose the menu path Edit→Classification.

The SAP system checks the classifications when saving, and displays a warning message if there are deviations: For example, if you attempt to assign a mass printing output device to a production printing spool server, the spool system compares the classification of the output device to the classification of the server. In the case that the classifications do not match, the SAP system informs you.