Location of disk journals on separate DASD devices from database files

Products

• IDMS
• IDMS - Database

Issue/Introduction

Using EMC DASD, the application and journal files are located on different logical devices to minimize I/O contention, based on recommendations made by IDMS support long ago. The application files are SMS managed. 

With the new DASD is this still required? The plan is to rename and relocate the journal files to the same DASD as the application files. 

Are there any concerns with this?

Environment

Release: All supported releases.

Resolution

In the past, it was informally recommended that journals be on different packs than the database files. This was due to the fact that years ago disk packs had movable heads that did the reading and writing so there was a greater possibility of contention.

In more modern devices, that switching is all electronic so the contention would be much less.

This has never been tested and there are no plans to do so.

It should be OK to move the journals and databases to the same DASD as this should not cause any performance problems. 

If there is an increase in the length of time for I/O waits after the change, it may be due to some level of contention. It is unlikely to be measurable. 

Report any results to IDMS support