Two of the most significant hardware performance enhancements in the history of the S/38 and AS/400 are the n-way processors and write-cached disk I/O processors (IOPs).
If you want optimum disk-write performance and you’re using the older disk IOPs that have 4 MB of write cache, spread your journal receiver disk arms over as many of these IOPs as you can (no more than five arms per IOP). If you’re using the 26 MB write cache disk IOPs, you can put more arms under the control of one IOP and achieve good results.
Spreading the receivers over multiple arms and using the 26 MB write cache provides a large amount of memory for the write-intensive journal receiver operations. Using the IOP’s write cache to the fullest lets the job or task that issues a journal write see a very short disk-write response time (one or two milliseconds) before continuing processing.
Note that the output data record may stay in the IOP’s write cache for several milliseconds (sometimes up to 200) before it’s written. When this occurs, it’s usually because there’s other data in the cache that arrived earlier. Because each IOP write cache has a separately powered backup memory, you don’t have a potential integrity problem.
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