Sami,
In addition to Volker's response, to which I heartily agree, there is a lot of context that is difficult to communicate in an ITRC Forum.
Outside of context, what is "high rate"? On some older systems, a hundred IOs/second was a "high" rate. On today's systems, where it is not uncommon to have many processes, a thousand IOs/second is not outrageous across the entire system. For that matter, with caching and memory-resident disks, certain rates are quite reasonable.
At the other end of the range, I remember one memorable program (admittedly this was nearly 30 years ago). This program wanted wrote tens (probably hundreds) of thousands of characters to the terminal, one character at a time using QIO (e.g., it was doing thousands upon thousands of buffered IO operations to the terminal). That activity brought a VAX-11/780 to a (pardon the pun) virtual halt. In that case the user was "persuaded" to modify their program.
Doing a simple DIRECTORY/FULL/OUTPUT=NL: SYS$SYSDEVICE:[*...] is illustrative (albeit for direct IOs). Even a simple AlphaStation 200 4/233 (certainly not the fastest system out there) can hit approximately 500 Direct IO/second with an RZ-28M internal drive. Buffered IOs, which can be any number of things, can accumulate faster.
Is this a sustained rate? What is the hardware? What are the details of the workload? What is the workload doing? All of these are critical to understanding the difference between a correctly tuned, but heavily worked system and a system that is being used efficiently.
Some of these questions are easily discussed in an online forum (e.g., type of CPU, OS release, what is the actual rate). Other questions (e.g., the details of the workload) are harder if not impossible to assess effectively in a forum such as this.
As has been suggested previously in other threads, resolving performance questions often require a great deal of background knowledge, or very experienced assistance [Disclosure: our firm does provide services in this area].
I was once called in and informed that a VAX system was promised to be fast, but took literally minutes to simply login. To say that the manager involved was upset is very much an understatement. When I arrived, and he demonstrated it for me, I was mystified at first. I could not think what would cause such a long login time on what appeared to be an idle machine. He had even volunteered that they had tried adding memory, but it had not helped performance.
Then a thought struck me. I went to a console, and used AUTHORIZE to display one of the accounts. Sure enough, the Working Set limits were set to approximately 200 pages (100Kbytes on a VAX). I reset the limit to a more reasonable number, and "performance" increased by a very large factor (1000x).
In performance, almost every question depends dramatically on the details. Sometimes, a situation is familiar enough that others have been down the same path. Other times, it is far more a question of understanding exactly what is actually happening and how it can be improved.
- Bob Gezelter,
http://www.rlgsc.com
