Planning parallel backup paths and servers

Data Protection for SAP can use several communication links between IBM Storage Protect™ clients to control alternate backup paths and alternate backup servers. This feature can increase throughput by transferring data over multiple paths simultaneously or to and from several servers in parallel. It can improve the availability of the IBM Storage Protect client-to-server communication and enable disaster recovery backup to a remote IBM Storage Protect server.

In Data Protection for SAP terminology, path denotes a connection between an IBM Storage Protect client or node, and an IBM Storage Protect server. A set of communication parameters is set for each defined communication path. An IBM Storage Protect server network address is an example of a communication path. This set of communication parameters is called client option data and is collected under a logical server name. The logical server name is determined by the user. On UNIX™ or Linux™ systems, all client option data can be stored in a single file. This file is the client system option dsm.sys file. On Windows™ systems, the client option data for each logical server must be stored in separate client option files that have the file name servername.opt. For example, if there are two logical IBM Storage Protect servers fast and slow, then two client option files fast.opt and slow.opt are required. Windows also requires an extra client user option file, dsm.opt. All option files must be in the same directory.

Each path in the initSID.utl profile is defined by a server statement and the corresponding definitions in the IBM Storage Protect client system option file dsm.sys (UNIX and Linux) or server.opt (Windows). The SERVER <server 1..n> statement denotes IBM Storage Protect servers that are defined in the Data Protection for SAP profile. This definition corresponds to the statement SERVERNAME server 1..n in the IBM Storage Protect client option file or files.

These servers are identified by their TCPSERVERADDRESS and can be on one system (multiple paths) or several systems (multiple servers). SESSIONS denotes the number of parallel sessions that Data Protection for SAP schedules for the path. If only one path is used, SESSIONS must be equal to MAX_SESSIONS, which specifies the total number of parallel sessions to be used (equivalent to number of tape drives/management classes). Data Protection for SAP attempts to communicate with the IBM Storage Protect server by using the first path in the profile.

If this attempt is successful, Data Protection for SAP starts the number of parallel sessions as specified for this path. If the attempt was unsuccessful, this path is skipped and Data Protection for SAP continues to the next path. This process continues until as many sessions are active as were specified in the total session number (MAX_SESSIONS). If this number is never reached (for example, because several paths were inactive), Data Protection for SAP ends the backup job.