Multiplexing when Duplicating Disk to Tape

Hi,

 

You don't need to multiplex/demultiplex,remulitplex when you're going from Disk to Tape, and as Rasheed stated, Disk backups are never multiplexed. The reason being that tape is a sequential storage medium, while disk uses random access. This means disk can read and write anywhere on the disk. Where it actually reads from, and writes to, is controlled by the file system really.

 

Mulitplexing was designed so you can do multiple backups at the same time to the same tape. If this wasn't available, you'd need to wait for 1 backup to complete before running another. As you can imagine, this is not the case with disk, if you copy two files to the same disk, they are able to copy at the same time. In effect, the file system is multiplexing the files onto the disk (file system) for you. Therefore, netbackup doesn't need to worry about it.

 

So when talking about disk, from a netbackup point of view, the images are separate and not mushed up together as on tape. But on another layer, "underneath" the file system, or if you look at the blocks on the disk, it is mushed up.

 

Make sense?

Thanks guys,

Is there anything that I should be tuning then to duplicate quicker to tape from disk as at the moment I only have 8 tape drives in a library and end up with lots of Duplication jobs queuing up as I can't write more than 8 at ony one time?

Hi,

 

You could play around with buffers sizes to improve the overall performance of disk and tape, but aside from that, not a lot more. Look for the netbackup performance tuning guide (might be from previous versions but the content is still relevant).