How much additional space would repair database require

[Apoorva]

Hello All,

We have a single node mongo (version 2.0.1) instance. We are running
out of disk space even after daily archiving as mongo doesn't return
the space back to the OS and tries to use it itself. Currently our
setup has become very sparse with around 50% space lying idle. You can
see that data + index size is around 1170 GB while storage size is
around 2158 GB and file size is around 2368 GB.
> db.stats()
{
"db" : "default",
"collections" : 106,
"objects" : 553988389,
"avgObjSize" : 2094.1392962010254,
"dataSize" : NumberLong("1160128855044"),
"storageSize" : NumberLong("2315777236208"),
"numExtents" : 1487,
"indexes" : 107,
"indexSize" : 97914435136,
"fileSize" : NumberLong("2543459500032"),
"nsSizeMB" : 16,
"ok" : 1
}

We want to reclaim the space and as this is not a mission critical
system (its like a dumping yard for logs) can sustain a downtime. We
don't want to spend on creating a replica set also we are in a
physical datacenter hence will prefer not to attach additional disk
only for repairing database. I want to understand :-
-How much free disk space is required for repair database
-How much space can we hope to recover after repair database
-Around how much time should it take to repair database.
-If at all repair database keeps going on, is it safe to just kill it
and restart the database.

Bulk of our data lie in a single collection so whether compact
collection would be better than repair database.

[gregor]

http://stackoverflow.com/questions/14472182/how-much-additional-space-would-repair-database-require/14478248#14478248