Mongodb write performance/load primary vs secondary

Question

In a replicated Mongodb environment, is the write performance/load on the secondaries the same as the primaries? If so, or not, why?

Edit: By writes to the secondary I am referring to the automatic propagation of the writes from the primary to the secondary.

Edit2: To help guide the conversation http://docs.mongodb.org/manual/core/replica-set-sync/#multithreaded-replication might suggest that write performance from the primaries to the secondaries might be better since they are performed in batch .

Answer 1

If by load you mean only writes in an isolated or off-peak system then it must be an uninteresting and similar performance/write . and almost who cares. However, in a working system where you have concurrent reads and writes then no. because one can alter that performance/readwrite if you use a 'read preference' of "secondary" or "secondary preferred" (heck, anything but "primary"). Under this scenario a replica set with 11 secondaries and 1 primary one can clearly see that any single secondary has a fraction of cpu/memory/disk/etc competition not only disk contention than the single primary. Recall that the default mode is brutal on the primary. here the secondaries exist only for redundancy vs high-availability.

primary Default mode. All operations read from the current replica set primary.

One can think of a RAID system whereby mirroring increases redundancy while striping increases performance. (True, not exactly the same mechanics but from the user's pov its a similar result in terms of reads. Sharding is closer to a RAID with striping) Using the default read preference of 'primary' one taps only into mirroring; using a read preference of 'secondary' you tap into the greater throughput.