Q

Moving journals to AS/400's that are mirrored.

We have two AS/400's that are mirrored. We want to move all the journals and receivers to another ASP. Can you

think of any implications?


It is a very good idea to have your journal receivers in separate ASP's. Their is no performance implication to leaving the journal object itself in the same library and ASP as the files being journaled though. In fact leaving the journal with the files makes it easier to restore the data from backup.

Create a separate ASP for each journal if possible. Mixing the receivers for several different journals in one ASP will result in poorer performance.

The best journal performance can also be obtained by placing the receivers for each journal in a "MIRRORED" ASP. Mirrored protected disks are preferable to RAID protected disks because writing journal data to a RAID disk results in the disk arm swinging between the outer and inner part of the disk drive as RAID striping is updated. I can't remember exactly which way it is, but I believe the RAID striping data is written to the outer part of the disk while the receiver data is written to the inner part.

If your journal environment is very active, utilizing as many disks arms as possible will always improve performance. On version 4.5 a new receiver size option was introduced, *MAXOPT1. This journal option not only allows you to have receivers up to 1 terabyte in size, it also allows for receiver data to be written to 100 disks at a time. Prior to this feature, the maximum number of arms used by journaling was limited to the 10 fastest arms in an ASP.

If you are by chance using remote journaling to synchronize transactions between your mirrored systems, it is best to configure exactly the same number of disk arms in each ASP on both systems. Remote journaling will only use the number of arms it uses on the source system when the transactions are replicated to the target system, even if you have more arms in the target system's ASP. I've had discussions with IBM on this and have been told that it is just a "quirk" of remote journaling.

In summary, the only negative implications to using separate ASP's for your journal receivers is NOT to use them.


This was first published in July 2001

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