Take the 2-minute tour ×  I copy a collection to another
collection. Data is 14GB. I deleted the copied collection. Yet
the size of the directory is still 14 GB.  I chose repair but it
seems to take forever. Actually inserting the whole data took
only 20 minutes and the repair is still running till now.  It's
just compacting data.  What happen if I do not repair the
database? Will files eventually be compacted?  share|improve
this question  2 Answers 2  up vote 3 down vote accepted  When
you delete data like this, the files are not automatically
rewritten to reflect the new size of the data (which is
potentially a massive operation). Instead, the free space in
those files is marked as free and will be re-used when you
insert new data.  As you have found, the only way to reclaim
that space on disk at the moment is a repair - that is not "just
compacting data". In fact a repair rewrites your data files from
scratch, essentially creating a brand new copy of them on
another part of the disk before removing the ol