If you've tried to make a backup of your zimbra installation by taring /opt/zimbra you may have noticed the output either fills your available storage or is 80 gigs larger than the actual Zimbra installation.

This is caused by an 80 gig sparse file:

-rw------- zimbra/zimbra 85899345920 2013-03-10 19:40 /opt/zimbra/data/ldap/mdb/db/data.mdb

# ls -lsah /opt/zimbra/data/ldap/mdb/db/
5.6M -rw-------. 1 zimbra zimbra  80G Mar 10 19:40 data.mdb

This appears to be a new feature of Zimbra 8 that was introduced for performance reasons (https://wiki.zimbra.com/wiki/OpenLDAP_Performance_Tuning_8.0#Notes_on_MDB). We can get around it by telling tar to account for sparse-ness:

# tar -Scf zimbra.tar /opt/zimbra/