[CentOS] Multipath and iSCSI Targets

Just started messing with multipath against an iSCSI target with 4 nics.
What should one expect as behavior when paths start failing? My lab setup
was copying some data on a mounted block device when I dropped 3 of 4 paths
and the responsiveness of the server completely tanked for several minutes.

Is that still expected?

Thanks,
jlc