When you have a RAID controller managing an array over a large amount of disks in an external chassis with a SAS expander, what happens if someone accidentally powers off the external chassis or accidentally unplugs the cable? What's the worst and most likely cases in terms of data integrity in the array?
Given that, you're asking the same question as, "What would happen if I pulled a group of disks out of a running system?"
The answer is probably data loss, frustration and downtime... Don't let it happen.
- Note, expanders are usually in the backplanes of external JBOD enclosures.