A DASD-only log stream has a single-system scope; only one system at a time can connect to a DASD-only log stream. Multiple applications from the same system can, however, simultaneously connect to a DASD-only log stream. No coupling facility is needed for a DASD-only log stream.

When a system logger application writes a log block to a DASD-only log stream, the system logger writes it first to the local storage buffers for the system and duplexes it to the DASD staging data set associated with the log stream. When the DASD staging data set's space allocated for the log stream reaches the installation-defined threshold, the system logger offloads the log blocks from its local storage buffers to VSAM linear data sets. From a user's point of view, the actual location of the log data in the log stream is transparent.

Both a DASD-only log stream and a coupling facility log stream can have data in multiple DASD log data sets; as a log stream fills log data sets on DASD, the system logger automatically allocates new ones for the log stream.

If you use DASD-only log streams, performance problems can easily occur. In general, you should use the coupling facility for all production log streams because you must set up the coupling facility for DFSMStvs locking anyway.

Recommendation: Do not use DASD-only log streams for the log of logs or for forward recovery logs in a multisystem sysplex environment because they cannot be shared. The first system that opened a data set would be able to use the logs, but any subsequent opens on other systems would fail because they could not connect to the forward recovery logs.