NDMP Backup running slow

Hi Experts,

There are are two backup jobs out of 19 jobs that are running extremely slow if i run them on different schedule.

Backup Tool:backup exec 2012

Tape Library :quantum scalar(LTO5)

I was unable to run those jobs on last weekend which was there scheduled run.Now i trie to run those jobs on this weekend but the spped is extremely slow.I checked the history and found that this is common problem for these backups.

I chceked with storae team they said there is no issue from there side.My drive is directly connected via FC.

Kindly advice what could be the probable reason and where i could change any settings to improve thorughput.

Regards

Automation