When one of masters is unreachable all other replica sets work too slow in mongodb 2.6.11, also I can not list the databases on mongos servers, and that is because of one replica set. How to solve this problem.
I have found this https://jira.mongodb.org/browse/SERVER-7246, do they say “If you have no redundant network connection to remote site, then go to hell”?
Replica sets are individual entities unless you are sharing resources among them like CPU,RAM,Disk… running multiple mongods in a single server.
I believe your case is that on a sharded cluster scatter-gather queries speed is determined by the slowest shard, so when one shard gets slow all scatter-gather queries will turn slow.
Upgrading to 3.0.7 and switching to wiredtiger solved this issue.