Managing persistent store space

Hi

I have a single instance of ActiveMQ v5.9 using persistent store and we are
constantly running out of space.
We use persistent messages with KahaDB and have 50gb store defined.
The queues directory only actually contains 26GB, but ActiveMQ admin says
"Store percent used 94", is that right?
Browsing the number of pending messages in queues, there is no way there is
26GB or 50GB worth of data!

I have noticed that we have lots of ActiveMQ.Advisory.Consumer.Queue.*
topics, which we don't use, but we use the advisoryWhenFull="true" in
conjuction with sendFailIfNoSpace="true" so that we get notified when
messages can't be queued. We also expire messages after 30 days, in hope
they will get deleted. If I disable advisory message am I going to lose
these two functions?

Any ideas?

Here are the relevant bits from our activemq.xml:
<bean id="store"
class="org.apache.activemq.store.kahadb.KahaDBPersistenceAdapter" >
<property name="directory" value="/opt/xyz/queues" />
<property name="journalMaxFileLength" value="3145728" />
<property name="checkpointInterval" value="5000" />
<property name="cleanupInterval" value="5000" />
</bean>

<broker xmlns="http://activemq.apache.org/schema/core"
useJmx="true" brokerName="localhost" dataDirectory="/opt/xyz/queues"
persistenceAdapter="#store">
<destinationPolicy>
<policyMap>
<policyEntries>
<policyEntry topic=">">
<deadLetterStrategy>
<sharedDeadLetterStrategy processExpired="false"/>
</deadLetterStrategy>
</policyEntry>
<policyEntry queue=">" cursorMemoryHighWaterMark="90" maxPageSize="10000"
queuePrefetch="10000" producerFlowControl="false" advisoryWhenFull="true">
<pendingQueuePolicy>
<storeCursor/>
</pendingQueuePolicy>
</policyEntry>
</policyEntries>
</policyMap>
</destinationPolicy>
<systemUsage>
<systemUsage sendFailIfNoSpace="true">
<memoryUsage>
<memoryUsage limit = "8 gb"/>
</memoryUsage>
<storeUsage>
<storeUsage limit="50 gb" store="#store"/>
</storeUsage>
<tempUsage>
<tempUsage limit="10 gb"/>
</tempUsage>
</systemUsage>
</systemUsage>
<plugins>
<timeStampingBrokerPlugin
zeroExpirationOverride="2419200000"/>
<discardingDLQBrokerPlugin dropAll="true"
dropTemporaryTopics="true" dropTemporaryQueues="true" />
</plugins>

</broker>