This is called "pinning the log."  It happens when a single transaction
takes a long time.  The log is circular starting anywhere within the log
volumes.  When a transaction starts an entry is placed into the log.  Other
entries, for other transactions, follow.  Finally, when the first
transaction is complete, the transaction is committed to the database.  That
frees the beginning of the log to move forward.  So very long running
transactions, like client database backups, will pin the log.  In high
transaction rate enviroments this can become a problem.  One way to avoid
this (to some extent) is to separate long running backups from high volume
backups: start your database backups after or long before your file server
backups, for instance.  It isn't the long running guy that gets you but
rather all the little ones while it's running.

Kelly J. Lipp
Storage Solutions Specialists, Inc.
PO Box 51313
Colorado Springs, CO 80949
lipp AT storsol DOT com or kelly.lipp AT storserver DOT com
www.storsol.com or www.storserver.com
(719)531-5926
Fax: (240)539-7175