Acronis backup from gigabit NAS to internal SCSI LTO-3 tape is very slow

I use Acronis True Image Server 9.1 (newest build) to backup the 15k SAS drives of a Windows Small Business Server 2003 to a Netgear ReadyNAS RNR4450 which takes not a long time to backup. I use a gigabit ethernet between NAS and Windows Server. Backup size is approx. 110GB.
Then if I store the backup-file to a HP Ultrium 920i TV Tape Drive connected directly via a dedicated HP Host Bus Adapter SCSI U320 to the Server backup takes approx. 9 hours for 100GB. (I use also acronis for that) Same speed for restore.
If I use the "Device Performance Test" of "HP Storage Library and Tape Tools" I get above 50MB/s for read and write from and to tape, doesn't matter whether compression activated or not. If I assume this values are correct a backup should take 1 hour worst but not 9 hours.
I also tested read performance from NAS which is 20MB/s and from internal SAS which is 78MB/s.
I deactivated Kaspersky Antivirus to not to influence performance.

Thanks for your help in advance,
RobertStart Free Trial