Ceph

http://workbench.dachary.org/ceph/ceph/blob/giant/src/mon/OSDMonitor.cc#L4007 runs tests by trying to map from min_size to max_size items for each ruleset. The default erasure code ruleset is:

rule erasure-code {
    ruleset 6
    type erasure
    min_size 3
    max_size 20
    step set_chooseleaf_tries 5
    step take default
    step chooseleaf indep 0 type host
    step emit
}

In a cluster with too few OSDs, each attempt to map more OSDs than available will exhaust all retries (50) which turns out to be expensive. In a cluster with 9 OSDs, it takes 5seconds.

$ time crushtool -i /tmp/crushhost --test --show-bad-mappings --rule 6 
user    0m4.921s

Since the test blocks the MON leader, it a few erasure coded rulesets will block the monitor long enough to exceed the timeouts and it will trigger an election.