HP 3000 Manuals HP 3000 Manuals
High End System Performance Considerations by Tim Canepa Commercial Systems Division As processor speed increases so does the relative load placed on the system. There are a few items to keep in mind when configuring your new high end HP 3000/980 system. Since the IO bandwidth on the newer machines is basically unchanged, you may want to consider a few simple guidelines when adding memory and disk storage to your system. The working set for a particular application will probably occupy a somewhat static portion of main memory. The user working set, however, will occupy space based on the number of active processes running the application. If your memory does not scale sufficiently to support the new user working set load, an unusually high level of swapping activity may result, causing a decrease in overall system performance. For example, if the user working set occupies .6MB per user and the application working set is 30MB, a 200 user system will require approximately 150MB, not counting the overhead required by the system. If you jump to 400 users, the working set space will occupy approximately 270MB (.6 x 400 + 30). Attempting to run the 400 users in 192MB will probably result in sluggish response times. By scaling the memory size appropriately, you will avoid unnecessary disk IO caused by swapping transient space to disk. Mixing disk sizes should be carefully monitored to achieve higher performance levels. If different size disks are used within the same volume set, your performance will probably improve if the master volume is one of the smaller disks (unless it is a 7935, which is relatively slow). The master disk of a volume set has a higher volume of disk traffic due to the number and type of system structures that reside on it (the transaction management logs reside on the master volume of a volume set). Because the general disk space management policy allocates extents on the disk with the most free space, larger disks tend to fill up faster (percentage wise) than smaller disks in the same volume set. This causes the larger disks to incur more IO traffic than the smaller ones. Since your master volume already has a high level of IO traffic, using a larger disk as the master will probably decrease your overall performance if the rest of the disks in the set are smaller. This situation can be compensated through the addition of memory, depending on the application working set. If you have a volume set that mixes disks with sizes of 1.3GB (5239568 sectors) and 544MB (2232192 sectors) you can expect the distribution of space to be somewhat unbalanced. The larger sized disks have 3007376 more sectors of capacity thus will receive the major portion of the extent allocations as well as the majority of IO traffic. If the larger disks are on a faster link (fiber link verses HP-IB) than the smaller disks, the increased IO activity may be overcome by the high performance link. A general rule would be to make larger capacity disks members, rather than masters if the disks in the volume set are using the same type of link.