location of Disk Journals on separate DASD devices from database files
Article ID: 101532
IDMSIDMS - DatabaseIDMS - ADS
We are using EMC DASD. Our application files and journals file are located on different logical devices to minimize I/O contention, based on recommendations made by CA long ago. The application files are SMS managed.
With the new DASD is this still required? We are considering renaming and relocating our journal files to the same DASD as the application files.
In the past we informally did recommend 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. Our understanding is that in today’s devices that switching is all electronic so the contention would be much less. We have never tested this and there are no plans to do so. Go ahead with your plan as we believe as you do that this will not cause any performance problems.
If you see an increase in the length of time for I/O waits after the change it may be due to some level of contention. We doubt that it would be measurable.