multiplexing and tape-to-tape duplication
What doesn't make sense here is that someone directed them to tape because disk was slow. Its usually the other way around. Disk was introduced into backup to lighten the load on tape drives when it came to clients with low performance. You would back it up to disk at trickle speeds, then stream it off disk onto tape a high rate.
From what you say it does sound like you have a very slow client as the MPX 1 meant it took long. The benefit of MPX 4 is that you can squeeze 4x times (theoretically) the performance out of the client.
Any ways, duplication to tape would be NON MPX as it reads the image,and duplicates it, it doesn't ready the tape (by default).
-mpx
Specifies that when you duplicate multiplexed backups, NetBackup creates multiplexed backups on the destination media, which reduces the time to duplicate multiplexed backups.
Multiplexed duplication is not supported for the following operations:
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Non-multiplexed backups
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Backups from disk type storage units
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Backups to disk type storage units
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FlashBackup or NDMP backups
If backups in the previous categories are encountered during duplication, NetBackup duplicates them first and uses non-multiplexed duplication. It then duplicates the multiplexed backups by using multiplexed duplication.If all the backups in a multiplexed group are not duplicated, the duplicated multiplexed group has a different fragment layout. (A multiplexed group is a set of backups that are multiplexed together during a single multiplexing session.)
If this option is not specified, all backups are duplicated by using non-multiplexed duplication.
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