Why does Sling/Jackrabbit use twice the disc space to store a file? - jackrabbit

Question

Why does Sling/Jackrabbit use twice the disc space to store a file and what can I do to prevent it from doing this?
I'm working on a project where we're storing files and associated data in Sling. For operational reasons we would like to avoid excessive disc usage. We've hit a problem where anytime we store a file in Sling the amount of disc space used appears to be double.
For instance, I have 47 megs of files. When uploaded to Sling I have 53 megs in the datastore, there's a lot of different files so I can accept that amount of inflation. However if we look at the total size of the Jackrabbit repository we see a different story ...
jackrabbit]# du -s
118688 .
jackrabbit]# du -s repository/datastore/
53296 repository/datastore/
jackrabbit]# du -s workspaces/default/blobs/
53464 workspaces/default/blobs/
Now the data associated with these files is quite small (<1 meg) so I don't see why the workspace is storing so much data when it's supposed to be all stored in the datastore. This problem gets worse when I upload a larger file, here I've added a 277 meg file to the above repository.
jackrabbit]# du -s
686508 .
jackrabbit]# du -s repository/datastore/
337152 repository/datastore/
jackrabbit]# du -s workspaces/default/blobs/
337320 workspaces/default/blobs/
I've uploaded sets of multi gigabyte files and this behaviour seems to be consistent.
I'm using the default repository.xml file created by the Sling standalone 6 when its run, this does appear to have the FileDataStore configured (see below). I was under the impression that with the FileDataStore configured Jackrabbit wouldn't store its files in blobs but that appears to be the case here. Can anyone provide me with a reason why this behaviour is exibited or a way to disable it? It seems exceedingly strange that a system would essentially store a file twice.
<Repository>
<FileSystem class="org.apache.jackrabbit.core.fs.local.LocalFileSystem">
<param name="path" value="${rep.home}/repository"/>
</FileSystem>
<DataStore class="org.apache.jackrabbit.core.data.FileDataStore"/>
<Security appName="Jackrabbit">
<SecurityManager class="org.apache.jackrabbit.core.DefaultSecurityManager" workspaceName="security">
</SecurityManager>
<AccessManager class="org.apache.sling.jcr.jackrabbit.server.impl.security.PluggableDefaultAccessManager">
</AccessManager>
<LoginModule class="org.apache.sling.jcr.jackrabbit.server.impl.security.PluggableDefaultLoginModule">
<param name="anonymousId" value="anonymous"/>
<param name="adminId" value="admin"/>
</LoginModule>
</Security>
<Workspaces rootPath="${rep.home}/workspaces" defaultWorkspace="default"/>
<Workspace name="${wsp.name}">
<FileSystem class="org.apache.jackrabbit.core.fs.local.LocalFileSystem">
<param name="path" value="${wsp.home}"/>
</FileSystem>
<PersistenceManager class="org.apache.jackrabbit.core.persistence.db.DerbyPersistenceManager">
<param name="url" value="jdbc:derby:${wsp.home}/db;create=true"/>
<param name="schemaObjectPrefix" value="${wsp.name}_"/>
<param name="shutdownOnClose" value="false"/>
</PersistenceManager>
<SearchIndex class="org.apache.jackrabbit.core.query.lucene.SearchIndex">
<param name="path" value="${wsp.home}/index"/>
<param name="supportHighlighting" value="true"/>
</SearchIndex>
</Workspace>
<Versioning rootPath="${rep.home}/version">
<FileSystem class="org.apache.jackrabbit.core.fs.local.LocalFileSystem">
<param name="path" value="${rep.home}/version" />
</FileSystem>
<PersistenceManager class="org.apache.jackrabbit.core.persistence.db.DerbyPersistenceManager">
<param name="url" value="jdbc:derby:${rep.home}/version/db;create=true"/>
<param name="schemaObjectPrefix" value="version_"/>
<param name="shutdownOnClose" value="false"/>
</PersistenceManager>
</Versioning>
<SearchIndex class="org.apache.jackrabbit.core.query.lucene.SearchIndex">
<param name="path" value="${rep.home}/repository/index"/>
<param name="supportHighlighting" value="true"/>
</SearchIndex>
</Repository>