Error when mount the database in exchange 2010 SP1

My company have two exchange 2010 SP1 servers with DAG configuration with OS widows server 2008 R2 in testing entironment.

Today i want to test my backup possibility, so i restore the backup data to another location not original location. I dismount the database and then delete the all files under the database location. last I copy back the files from back up location to database location. When i want to mount the database. It will come out the below error!

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Microsoft Exchange Error
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Failed to mount database 'mail2'.
mail2FailedError:

Couldn't mount the database that you specified. Specified database: mail2; 
Error code: An Active Manager operation failed. Error: The database action failed. 
Error: Operation failed with message: MapiExceptionCallFailed: Unable to mount
database. (hr=0x80004005, ec=1011)

[Database: mail2, Server: mail2.e0594.cn].

An Active Manager operation failed. Error: The database action failed. 
Error: Operation failed with message: MapiExceptionCallFailed: Unable to mount
database. (hr=0x80004005, ec=1011)

[Database: mail2, Server: mail2.e0594.cn]

An Active Manager operation failed. Error: Operation failed with message: 
MapiExceptionCallFailed: Unable to mount database. (hr=0x80004005, ec=1011)

[Server: mail2.e0594.cn]

MapiExceptionCallFailed: Unable to mount database. (hr=0x80004005, ec=1011)

Any suggestion? Thanks!

Exchange is usually really good at telling you why something weird is happening. Check your Application event log at the time you try to mount the database and see what it says.

You don't specify if you mounted the database with the Exchange Management Console or the Exchange Management Shell. If you didn't use the shell, try mounting the database with the shell using Mount-Database "Mailbox Database Name" - that may give you a different or more descriptive error.

My initial suspicion (this is an educated guess more than anything else) would be something to do with the transaction logs (you didn't say anything about restoring the logs back) - they might belong to the wrong database (the one you deleted).

I'm curious as to what backup method you're using, since you would usually restore into a recovery database and merge that with an active database. Your method of replacing the files will work, but would require the databases to be dismounted while they were backed up (this is not really commonplace). It could be that your backup is actually corrupt because you aren't using an Exchange aware backup agent.