How to increase the speed of RMAN backups

There could be several bottlenecks which makes our backups slower.

Last month we had similar situation and after investigating the issue in the legato side, the number of allocated tape drives seemed us small. Because of that we had increased the number of tape drives devoted for the backup job from 2 to 4.

Interestingly, it does not make any sense.

After than, we increased the number of channels in RMAN script from 8 to 12 and in this way we managed to increase the utilization of tape drives. The real reason behind was the utilization of tape drives are dependent on utilization of disks for reading.

Further, in legato side, while monitoring the backup job, only 2 of allocated 4 tape drives are used. The minimum session limit for each tape drive was 8. That means 12 channels opened only utilizes 2 tape drives. After setting minimum session value per tape drive in legato side to 3, we are happy with the picture we got. 12 channels of backup work is evenly distibuted across the 4 tape drives.

As a result, our full backup job now lasts for 20 hours, which was 50 hours before the optimization.