[Info-vax] How do I assign a disk to a CPU?

[Stephen Hoffman]

On 2020-10-18 14:54:57 +0000, Volker Halle said:

> you could use MONITOR MODE/CPU=0 to check the CPU utilization of your 
> primary CPU. If you see very high interrupt and kernel mode state 
> during heavy disk-IO, it might help to change the preferred CPU for the 
> fibre channel adapter/port.

And for various of these sorts of request cases, MONITOR 
DISK/ITEM=QUEUE tends to show queue length activity of 0.5 or higher.

Over the measured interval, a queue length of 0.5 means half of all I/O 
requests are waiting for a previous I/O to complete.

Queue length values of 0.5 and larger usually mean storage is saturated 
and apps are stalling, or less commonly means that the storage is 
failing.

Some OpenVMS app I/O can be continuous, but other app activity can be 
quite bursty.

Best to keep the queue length measurement intervals closer to the app 
run-time duration and/or to the times of heaviest I/O activity.

Amdahl's Law applies here.


-- 
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