Slow LTO4 tape drive

EDIT UPDATE: for others seeing this thread. For me the issue was the scsi card itself for some reason. I replaced the Adaptec with an LSI and it works great now

Regardless of if I'm backing up the local server or a "disk-disk-tape" the speed writing to the tape drive is only around 350-500MB/min (not sec…min).

That's painfully slow.

Hardware:

IBM x3630 server – 12GB RAM, Windows 2008 R2

• Here are the specs on the controller and drives:

  • 46M0916 (M5014 controller) supports up to 6 Gbps of performance
  throughput for each port at full duplex • 44W2234 (IBM 300GB 15K 6
  Gbps SAS 3.5-inch Hot-Swap HDD) supports: o Drive to host SAS
  interface that supports up to 6 Gb/s burst rate o Drive media to
  buffer interface that supports sustained interface data transfers of
  up to 204 MB/s • 42D0767 2 TB 7.2K rpm 6 Gbps NL SAS 3.5-inch HS HDD)
  supports: o Drive to host interface that supports up to 6.0 Gb/s
  burst rate o Drive media to buffer interface that supports sustained
  interface data transfers of up to 150 MB/s average

• SCSI Controller = Adaptec 29320LPE U320

• Tape Drive = HP Ultrium LT04 drive SCSI inside Overland Storage Arcvault 12

Things I've done so far:

• Updated the firmware
• Worked with BackupExec support to increase buffers, etc.
• Ran the HP Tape Tool software (results showed that the tape might be operating at u160 speed, and performance tests showed write speed around 9MB/sec

So, I'm at a loss. All of the hardware is decent and compatible. I'd love to just rip and replace but I'm also wanting to figure this out.

EDIT: also getting these errors on the HP Tape Tools:

The drive is experiencing polling (1.0 / sec. polling rate) on initiator ID 7.
Polling can interrupt the normal operation of the drive, and significantly reduce performance.

Don't know what that means though.