Unbalanced Performance To Library

[Ayman Altounji]

We have a TL891 with dual tape drives connected to a DL360 running NT4.0SP6a with BackupExec 8.5. When 2 backup jobs are created each backing up a section of a directory on one physical server, one job will perform at the normal throughput of 275Mb/I to the one drive while the second drive works at about 20Mb/s. The bottleneck doesn't appear to be the server's NC, or the CUP or memory. Does anyone know what may be causing the difference in performance?
Thanks