I upgraded a mongodb server from 1.6.5 to 1.8.0, and dropped the collection after the upgrade. After dropping the collection, the disk space used on the machine was not reclaimed.

show dbs;

still shows the total size of the db as it was before the collection drop (~783GB).

db.stats() shows the correct usage of the remaining collections:

"dataSize" : 188678580624, (roughly 175 GB)

db.stats() indicates that there are still 4 collections, even though there are only three remaining.

> db.stats()
{
"db" : "xxxx",
"collections" : 4,
"objects" : 149504141,
"avgObjSize" : 1262.0291275008897,
"dataSize" : 188678580624,
"storageSize" : 192878791072,
"numExtents" : 127,
"indexes" : 4,
"indexSize" : 26608217472,
"fileSize" : 841336487936,
"ok" : 1
}
> show collections;
p_201103
p_201104
system.indexes

> db.p_201103.stats()
{
"ns" : "xxxx.p_201103",
"count" : 155304251,
"size" : 196040069044,
"avgObjSize" : 1262.2968642629105,
"storageSize" : 198852279456,
"numExtents" : 127,
"nindexes" : 2,
"lastExtentSize" : 1991168256,
"paddingFactor" : 1.009999999999994,
"flags" : 1,
"totalIndexSize" : 27651591552,
"indexSizes" :

{ "_id_" : 6458263216, "url_1" : 21193328336 }

,
"ok" : 1
}

> db.p_201104.stats()
{
"ns" : "xxxx.p_201104",
"count" : 0,
"size" : 0,
"storageSize" : 8192,
"numExtents" : 1,
"nindexes" : 2,
"lastExtentSize" : 8192,
"paddingFactor" : 1,
"flags" : 1,
"totalIndexSize" : 16384,
"indexSizes" :

{ "_id_" : 8192, "url_1" : 8192 }

,
"ok" : 1
}

> db.system.indexes.stats()
{
"ns" : "xxxx.system.indexes",
"count" : 4,
"size" : 456,
"avgObjSize" : 114,
"storageSize" : 5120,
"numExtents" : 1,
"nindexes" : 0,
"lastExtentSize" : 5120,
"paddingFactor" : 1,
"flags" : 0,
"totalIndexSize" : 0,
"indexSizes" : {

},
"ok" : 1
}

This does not show anything for the dropped collection:

db.system.namespaces.find().toArray()
[

{ "name" : "xxxx.system.indexes" }

,

{ "name" : "xxxx.p_201103" }

,

{ "name" : "xxxx.p_201103.$_id_" }

,

{ "name" : "xxxx.p_201103.$url_1" }

,

{ "name" : "xxxx.p_201104" }

,

{ "name" : "xxxx.p_201104.$_id_" }

,

{ "name" : "xxxx.p_201104.$url_1" }

]

There do not appear to be any error messages in the log from the drop:

Mon Mar 21 20:16:28 [conn5387] CMD: drop xxxx.p
Mon Mar 21 20:16:29 [conn5387] query xxxx.$cmd ntoreturn:1 command:

{ drop: "p" }

reslen:155 987ms

The log seems normal for a few thousand lines after that (as far as I checked).

The server has not been shut down since the upgrade to 1.8.0, and I'm also running journaling on it now since the upgrade.
I have not changed the nssize.