Hi @KyungKee Kim 

Are we talking about WORM on hardware or software level?

@KyungKee Kim You can't reuse WORM LTO media, because as the names states it's designed to be tamper proof. So you can write/append data once and read-back many times. For VTL I would assume the vendor delivering the VTL capability has to support WORM and for a Commvault disk library it is fixed in software. So not sure where yo are looking for because for most of the it, it is outside of the boundaries of Commvault. 

@Jos Meijer The customer wants to set WORM in VTL hardware first, and then set Commvault accordingly.

@Onno van den Berg When all backup data stored in WORM tape media expires after the retention period, it is stated in the BOL that it is moved to the retired media pool. Is this tape media impossible to reuse after that?

Correct, you will not be able to re-use the media as it is designed as WORM media. Your thinking would leave an option on the table to influence the retention of the data and thus make the data unavailable. 

You can't erase WORM media.
You can't perform an overwrite of data on WORM media.
You cant; format WORM media unless the media is unformatted.
And I think you also cannot use multiplexing.