Of course it is. If systems administration would be simple we wouldn't be the heroes of the whole IT business, would we? So welcome to the job with the biggest demands and the greatest rewards our industry has to offer.

Well, this is something we can build on. I can help you better when i return to the office (and the documentation: there is a lot of detail i do not know from the top of my head).


A little general information about the disk statistics and what they mean:

Every disk has a "command queue": read- and write-requests are buffered and then worked on one after the other. If the queue is full the disk will not accept more commands until some room in the queue is free again. Keep this in mind for a moment.

The OS now asks every disk (in this regard, "disk" means "everything with a "hdisk"-device - it does not have to be a physical disk but also a LUN, a RAID-set, ....) in turn if this queue has length 0 at the moment or not, which the disk answers with "yes" (= length 0) or "no" (any length different then 0). From many of these answers the OS compiles a percentage which is shown as "disk busy %".

This means that "disk busy" is not as important as you think and that it has no meaning by itself. If a queue has "not length 0" it can have length 1 or length 15. The value is interesting because you get a measure of how many accesses a disk experiences. But you cannot measure the throughput of a device from that value alone. Disk operations come in different sizes, varying from 512 bytes (one disk block) up to several GB. Which of these is outstanding the busy% will not tell you, just that there is one outstanding at all.

You might consider balancing for "I/O" rather than for "busy%", but you might even do something different. I suggest you read my little introduction to performance tuning with emphasis to I/O-tuning in the meantime. I will come back to this thread once i am back in office (next Monday).

I hope this helps.

bakunin