Tape speed more than the max rate with multiplexing !? and a few more questions about it
- 3 years ago
Hi mhdganji
1: Writing speed for tape drives are typical without compression applied. Appling compression will increase the amount of incoming data required to make the tape drive running without start/stop operations. Always ensure incoming network bandwidth is larger that tape drive bandwidth
2: Using the activity monitor to get a picture, multiplexing complicates the picture. But in general the writing speed you see in the activity monitor is spot on.
3: Multiplexing basically mean multiples backup streams are written concurrent to the tape drive, to use the full bandwidth of the tape drive. However what you gain during backup, you loose during restore. Let's say backups are written with a MPX=4, and the backup are equally in size and delivered speed. then during restore 3/4 of the read data must be "throw away" during restore, causing increased restore speed. To make it worse, let's assume you have 3 really fast backup stream, and a really slow backup. Then the ration for data to be "throw away" for the slow backup, may be much worse. Bottom line, consider fragment size and MPX carefully. Large fragment sizes and large MPX is a really bad combo.
From a usage point of view, using multiplexed backup are safe to use. The technology has been in Netbackup for more than 22 years.4: The storage unit configuration has a max number of stream, that goes hand in hand with the policy configuration.