This was when executing db.metrics.drop() from the console.

> db.metrics.stats()
{
"sharded" : true,
"ns" : "sd.metrics",
"count" : 0,
"size" : 0,
"avgObjSize" : NaN,
"storageSize" : 24057095664,
"nindexes" : 2,
"nchunks" : 309,
"shards" : {
"shard1" : {
"ns" : "sd.metrics",
"count" : 0,
"size" : 0,
"storageSize" : 9916705280,
"numExtents" : 35,
"nindexes" : 2,
"lastExtentSize" : 1659307008,
"paddingFactor" : 1,
"flags" : 1,
"totalIndexSize" : 16384,
"indexSizes" :

{ "_id_" : 8192, "accId_1_sId_1" : 8192 }

,
"ok" : 1
},
"shard2" : {
"ns" : "sd.metrics",
"count" : 0,
"size" : 0,
"storageSize" : 14054300400,
"numExtents" : 37,
"nindexes" : 2,
"lastExtentSize" : 2146426864,
"paddingFactor" : 1,
"flags" : 0,
"totalIndexSize" : 16384,
"indexSizes" :

{ "_id_" : 8192, "accId_1_sId_1" : 8192 }

,
"ok" : 1
},
"shard3" : {
"ns" : "sd.metrics",
"count" : 0,
"size" : 0,
"storageSize" : 86089984,
"numExtents" : 11,
"nindexes" : 2,
"lastExtentSize" : 20872960,
"paddingFactor" : 1,
"flags" : 0,
"totalIndexSize" : 16384,
"indexSizes" :

{ "_id_" : 8192, "accId_1_sId_1" : 8192 }

,
"ok" : 1
}
},
"ok" : 1
}
> db.metrics.drop()
true

shard1 mongod log:

Thu Mar 10 10:53:14 [conn41486] getmore local.oplog.rs cid:2128519673161512587 getMore: { ts:

{ $gte: new Date(5580550324516552705) }

} bytes:20 nreturned:0 3150ms
Thu Mar 10 10:53:14 [conn21939] getmore local.oplog.rs cid:6381007320104569484 getMore: { ts:

{ $gte: new Date(5579959934017077250) }

} bytes:20 nreturned:0 3083ms
Thu Mar 10 10:53:21 [conn13403] query admin.$cmd ntoreturn:1 command:

{ writebacklisten: ObjectId('4d6efa1abaea80e510234bec') }

reslen:60 300035ms
Thu Mar 10 10:53:33 [conn59623] query sd.$cmd ntoreturn:1 command:

{ drop: "metrics" }

reslen:133 107ms
Thu Mar 10 10:53:33 [conn59623] wiping data for: sd.metrics
Thu Mar 10 10:53:39 [conn41486] getmore local.oplog.rs cid:2128519673161512587 getMore: { ts:

{ $gte: new Date(5580550324516552705) }

} bytes:20 nreturned:0 3491ms
Thu Mar 10 10:53:39 [conn21939] getmore local.oplog.rs cid:6381007320104569484 getMore: { ts:

{ $gte: new Date(5579959934017077250) }

} bytes:20 nreturned:0 3508ms
Thu Mar 10 10:53:46 [conn6603] query admin.$cmd ntoreturn:1 command:

{ writebacklisten: ObjectId('4d6ed83117d2d15d18d7bd20') }

reslen:60 300037ms
Thu Mar 10 10:53:55 [conn41486] getmore local.oplog.rs cid:2128519673161512587 getMore: { ts:

{ $gte: new Date(5580550324516552705) }

} bytes:20 nreturned:0 3500ms

shard2 mongod log:

Thu Mar 10 10:53:22 [conn50995] query admin.$cmd ntoreturn:1 command:

{ writebacklisten: ObjectId('4d6efa1abaea80e510234bec') }

reslen:60 300037ms
Thu Mar 10 10:53:33 [conn87546] query sd.$cmd ntoreturn:1 command:

{ drop: "metrics" }

reslen:133 121ms
Thu Mar 10 10:53:33 [conn95787] sd.metrics_110301 Assertion failure _c.get() db/query.cpp 425
0x55125e 0x562c61 0x652ad0 0x796fb6 0x79a115 0x79c644 0x79d1e7 0x64c89b 0x7df348 0x7dbc52 0x7dcb95 0x644c55 0x649191 0x757995 0x759ec0 0x8a65ee 0x8b6a30 0x36b980673d 0x36b8cd3f6d
/home/david/mongodb/latest/bin/mongod(_ZN5mongo12sayDbContextEPKc+0xae) [0x55125e]
/home/david/mongodb/latest/bin/mongod(_ZN5mongo8assertedEPKcS1_j+0x111) [0x562c61]
/home/david/mongodb/latest/bin/mongod(_ZN5mongo7CountOp8nscannedEv+0x40) [0x652ad0]
/home/david/mongodb/latest/bin/mongod(_ZN5mongo12QueryPlanSet6Runner3runEv+0xe86) [0x796fb6]
/home/david/mongodb/latest/bin/mongod(_ZN5mongo12QueryPlanSet5runOpERNS_7QueryOpE+0x255) [0x79a115]
/home/david/mongodb/latest/bin/mongod(_ZN5mongo16MultiPlanScanner9runOpOnceERNS_7QueryOpE+0x64) [0x79c644]
/home/david/mongodb/latest/bin/mongod(_ZN5mongo16MultiPlanScanner5runOpERNS_7QueryOpE+0x17) [0x79d1e7]
/home/david/mongodb/latest/bin/mongod(_ZN5mongo8runCountEPKcRKNS_7BSONObjERSs+0x3cb) [0x64c89b]
/home/david/mongodb/latest/bin/mongod(_ZN5mongo8CmdCount3runERKSsRNS_7BSONObjERSsRNS_14BSONObjBuilderEb+0xa8) [0x7df348]
/home/david/mongodb/latest/bin/mongod(_ZN5mongo11execCommandEPNS_7CommandERNS_6ClientEiPKcRNS_7BSONObjERNS_14BSONObjBuilderEb+0x9e2) [0x7dbc52]
/home/david/mongodb/latest/bin/mongod(_ZN5mongo12_runCommandsEPKcRNS_7BSONObjERNS_10BufBuilderERNS_14BSONObjBuilderEbi+0x895) [0x7dcb95]
/home/david/mongodb/latest/bin/mongod(_ZN5mongo11runCommandsEPKcRNS_7BSONObjERNS_5CurOpERNS_10BufBuilderERNS_14BSONObjBuilderEbi+0x35) [0x644c55]
/home/david/mongodb/latest/bin/mongod(ZN5mongo8runQueryERNS_7MessageERNS_12QueryMessageERNS_5CurOpES1+0x32e1) [0x649191]
/home/david/mongodb/latest/bin/mongod [0x757995]
/home/david/mongodb/latest/bin/mongod(_ZN5mongo16assembleResponseERNS_7MessageERNS_10DbResponseERKNS_8SockAddrE+0x5b0) [0x759ec0]
/home/david/mongodb/latest/bin/mongod(_ZN5mongo10connThreadEPNS_13MessagingPortE+0x21e) [0x8a65ee]
/home/david/mongodb/latest/bin/mongod(thread_proxy+0x80) [0x8b6a30]
/lib64/libpthread.so.0 [0x36b980673d]
/lib64/libc.so.6(clone+0x6d) [0x36b8cd3f6d]
Thu Mar 10 10:53:33 [conn87546] wiping data for: sd.metrics
Thu Mar 10 10:53:33 [conn95787] query sd.$cmd ntoreturn:1 command: { count: "metrics_110301", query:

{ p: false }

, fields: null } reslen:113 12431ms
Thu Mar 10 10:53:34 [conn87546] query admin.$cmd ntoreturn:1 command:

{ setShardVersion: "sd.metrics", configdb: "config1:27019", version: Timestamp 0|0, serverID: ObjectId('4d74b25af879e643c98372d5'), authoritative: true, shard: "shard2", shardHost: "set2/rs2a:27018,rs2b:27018" }

reslen:73 982ms

shard3 mongod:

Thu Mar 10 10:53:19 [conn52633] query admin.$cmd ntoreturn:1 command:

{ writebacklisten: ObjectId('4d6efa1abaea80e510234bec') }

reslen:60 300035ms
Thu Mar 10 10:53:19 [conn94822] query sd.metricsArchive ntoreturn:1 reslen:36 nscanned:0 { $query:

{ accId: 2461, metric: "loadAvrg", tA: new Date(1298851200000), sId: 35 }

} nreturned:0 228ms
Thu Mar 10 10:53:20 [conn94822] query sd.metricsArchive ntoreturn:1 reslen:36 nscanned:1 { $query:

{ accId: 4145, metric: "diskUsage", tA: new Date(1298851200000), iK: "/dev/shm", sId: 7 }

} nreturned:0 136ms
Thu Mar 10 10:53:34 [conn95383] wiping data for: sd.metrics
Thu Mar 10 10:53:42 [conn46990] query admin.$cmd ntoreturn:1 command:

{ writebacklisten: ObjectId('4d6ed83117d2d15d18d7bd20') }

reslen:60 300036ms
Thu Mar 10 10:53:42 [conn28244] query admin.$cmd ntoreturn:1 command:

{ writebacklisten: ObjectId('4d6be173f9824b3eeb5a29b5') }

reslen:60 300035ms
Thu Mar 10 10:53:55 [conn3040] query admin.$cmd ntoreturn:1 command:

{ writebacklisten: ObjectId('4d67ad9dd72169f9a6a566c7') }

reslen:60 300035ms
Thu Mar 10 10:54:47 [conn94063] update sd.metricsLatest query:

{ accId: 2391, sId: 3 }

143ms