26 webservers and only two mongodb instances? Seems stacked.. Why not set up more instances and split the load across them (sharding, splitting collections acro

26 webservers and only two mongodb instances? Seems stacked.. Why not set up more instances and split the load across them (sharding, splitting collections across replica sets, etc) or similar? Also - big question for me: were you using a ridiculously old version of mongo? I have yet to run into anyone who is on 2.0 or 1.8 and is still running master/slave (as opposed to replica sets). Sounds like your writes weren't working when you moved to replica sets because your client wasn't properly configured.