View Full Version : Multiplexing

October 23rd, 2008, 09:13 AM
How could I do backups like the Veritas NetBackup using the multiplexing records in tapes.
I didn't see anything about the multiplexing records at Zmanda.


October 26th, 2008, 10:39 AM
Multiplexing is mixing of data from different backup clients on tape. The purpose of multiplexing in products such as NetBackup and NetWorker is to feed data to a tape drive fast enough to avoid constant stopping and rewinding of a tape called shoe-shining.

Shoe-shining is bad because it reduces the throughput and shortens the life of both the media and the drive.

The multiplexing prevents shoe-shining, but it creates challenges for recovering your data:
- you are now locked into using NetBackup because you always need it to de-multiplex data
- multiplexing increases the amount of time required for the recovery. The more dumps from different clients are intermixed on tape (or other media) the longer it takes to recover the data, especially when you have to recover lots of data from different tapes.

Amanda keeps the tape drives streaming by using a staging area called holding disk.

The holding disk collects data from all clients and as soon as first backup is complete, it starts feeding data to tape at optimal speed assuming the hardware of the Amanda server can push it fast enough. You also recover your data very fast because you don’t waste time on de-multiplexing of backup images.

You can read about Amanda data formats, the holding disk and other advantages of Amanda by getting a free registration on Zmanda Network (http://network.zmanda.com/) and downloading “Amanda advantages over proprietary backup” white paper.
Dmitri Joukovski