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LTO-4 under HP-UX 11.11 and NBU 6.0mp4 - Poor Throughput?

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LTO-4 under HP-UX 11.11 and NBU 6.0mp4 - Poor Throughput?

Fibre Connected LTO Drives - currently with 2G connections.

When I use dd if=/dev/zero of=/dev/rmt/55mn (or BEST) -- with blocksizes ranging from 256k to 1024K, I am able to verify my LTO Drives are reaching their rated 2Gbit hookup speed of 100 to 120 MB/sec.

I have test filesystems -- also 2Gbit connected to a fast storrage array. dd test from both non-striped and concat show I am able to read close to Fibre Speed -- 100 to 120MB/sec.

Under NBU, I set up the LTO drives as HCART type per Symantec DOcumentation to use the latest Mapping File to auto-discover and type the drives -- which it did as type HCART.

But when backing up the filesystems I only get a mere 8 to 10 MB/sec. Even if I back up the raw device beneath the filesystem (using NBU Advanced CLient) -- my tput stays at 8 to 10 MB/sec.

However, I am able to stream up to 12 of these filesystems to just one LTO drive and still keep the same per filesystem throughput -- which means my LTOs are being fed and able to digest near or at its rated speed.

I am puzzled. Is my issue with NBU configuration? I think I have my SIZE_BUFFERS and NUMBER_SIZE_BUFFERS set up properly -- 25k and 32 currently.

Initially I thought it's my storage layout -- my VxVM or LVM stripes and configuration and kernel tunables but dd tests show those filesystems and volumes are capable of being read/sucked intensely. Why does NBU seem incapable of sucking data that intense?

Any advice?
Hakuna Matata.