cDOT strange disk assignment on 3rd disk shelf of a stack

[bbjholcomb]

We have four different cDOT systems that we noticed that all the drives primary path is all on one connection except for the 3rd disk shelf (node run local -command storage show disk -p).

For example, shelf 10 primary path 11a.10.x port B, shelf 11 the primary path 11a.11.x Port B, shelf 12 primary path 1a.12.0 port B, 11a.12.12.1 Port B, 1a.12.2 port A.

All the drives in the stack are assigned to ONE controller. We have different stacks and different type of shelves (SAS vs. BSAS), the same problem.

Config Advisor is clean. We are running 8.2P5.

[aborzenkov]

I am not aware of any way to manually designate primary path. For SAS shelves primary path was always selected on whole shelf basis, but different shelves in a stack normally are balanced between two adapters. I think I have seen different output, but it could have been in maintenance mode. I just briefly checked and all systems I have access to have whole shelf assigned to one primary path. System with 6 shelves in stack has them balanced between two adapters (3+3).

That’s different from FC shelves where primary path was selected per disk.

[bbjholcomb]

It appears this happens anytime there is an odd number of shelves in a stack.

If we have 2 or 4 shelves it's correct, if we have 3 or 7 the middle shelf will have every other disk on a different primary path.