What is a shared logical partition under z/OS?

Question

My understanding was that PR/SM allowed for a number of LPARs, each running its own copy of z/OS (or other OS).

However, one of IBMs performance reporting tools has a report entitled "CPU Busy by Shared LPARs".

Now we've always run this product on a single instance of z/OS, whether on its own LPAR or under z/VM so I'm trying to figure out what this is reporting. How exactly can LPARs be shared at all?

The main reason I'm asking is because I want to get a decent indication as to how a single LPAR is running (CPU% used). I want to make sure it's for that LPAR only, not somehow leaking information from another LPAR.

Answer 1

I'm not a z/os guru so what follows is just a wild guess...

I believe a many-to-many relationship exists between LPAR and CPU. A given LPAR can draw upon multiple CPU's and/or a single CPU can provide resources to multiple LPAR's. If you have multiple LPAR's running off of a given CPU, then is it possible that "CPU Busy by Shared LPARs" reflects how busy that CPU is as result of the LPARs that share it? In other words, the thing being shared is the CPU not the LPAR.