Simultaneous read-only snapshot mount

[Kevin Day]

It's now possible/somewhat common for the ability to have two systems can see the same disk(s) at the same time (through iSCSI or storage systems that support dual controllers, etc). 

Suppose system A has a filesystem mounted RW, and takes a snapshot. Can system B access that snapshot via a read only mount, while system A continues to read/write to that filesystem? Or more basically, is everything needed to read a snapshot stable/unchanging enough that a second system can read from it while the filesystem is still being updated?

-- Kevin