Miserable tape drive performance

[pshyvers]

I am working with 2 brand new HP LTO-4 drives (in quantum superloader 3's), but they are defying my every attempt at speed. I spent a few days messing with them, and last night I got raw performance in LTT (Zeroes) to 130MB/s, but this morning for no explainable reason it's dropped back to 65MB/s. At the time I thought backdating the firmware had fixed the problem (from B35Z to B22Z. Both provided by Quantum), but it's become clear that didn't fix it.

Currently they run a consitant 65MB/s for zero's and in the low 50's for the 2:1 and 4:1 data. I have stuck my ear to the drive as it writes, and it will whirr for a second and stop, whirr for a second and stop. The progress meter does the same thing; burst and pause, burst and pause.

The drives are hooked up to a pair of PC's that are above and beyond the requisite specs. They are using PCI-e x1 Ultra320 SCSI cards (Adaptec). Interestingly, the Health report says my connection speed is set at 160MB/s, which is concerning, but shouldn't be directly affecting my tests (the tapes can only write 120MB/s native)

My only other thoughts has been the fact that the card is in a PCI-e x16 slot, but I have read that when downplugging the worst case is the board drops the bus to x1- which is all my card needs! I also wonder if the PCI-e graphics card might be hogging bandwidth, but PCI-e has seperate bus lanes by definition, and dropping the graphics to 800x600x16 doesn't seem to help.

Thanks!

note: this is all w/ LTT's tape drive performance test

[Marino Meloni_1]

If you have such an inconsitent performance test result using LTT "device performance test" (that is not involving the disk at all, just generating data from the memory server to the drive) I suspect you may have cables or terminator that are not working well.
Part of the first dialogue between the HBA and the target (drive) is to allow a "domain validation" that mean that the speed will be decided based on some tests on data exchange.
The negotiated speed may change if cables are not good up on reboot.