NetApp Filer ==> LTO5 tape NDMP backup performance

Hello,

I have a NetApp 3270 filer that is protected by using two-tier NDMP mode. Datastream goes directly to IBM LTO5 tape drive via FC.

NDMP command

nsrndmp_save -T dump

NDMP settings on the client is as follows

DIRECT=Y

HIST=Y

UPDATE=Y

UTF8=Y

Default block size on nthe target tape drive is set to handler default (128k in my environment).

Backup takes 12 to 24 hours and backup speed varies 30 to 100 Megs/second.

I tried to directly set write block size to 256k - set it to the settings of target drive and added

NDMP_AUTO_BLOCK_SIZE=Y to the backup parameters.

Although write block increased, backup speed remained the same.

Is there any parameters on the NetApp side that can be set in order to boost NDMP server on the filer?