Exchnage2010 DAG and SanapManager for Exchange

Have a question regards to Exchnage GAG and its LUNssinc ei have little knowledge on both Exchnage2010 and SME.
As i understand there will be multiple copy of DB in more than two servers and logs are replayed to keep update copy of the database.
Here is my client place i noticed that they have three luns for each mailbox database , one for db, another one for db_log and another lun for log.
What this third pun for log?

Is this something to do with SME?
LVL 2
sara2000Asked:
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sara2000Author Commented:
This does explain the dag and its log, but does not say anything about the third log and db lun.
Is it something to do with lag copy?
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