# low bandwidth into a SDLT?



## monkeyboy (Jun 10, 2012)

I recently set up a machine running FreeBSD 8.2 and just tried running a Quantum SDLT drive on an Adaptec 2940W. Using a blocking factor of 50KB, with dump, tar or just dd, I seem to only be getting about 350KB/s. On a similar machine with a DLT drive I get at least 1200KB/s.

Any clues as to why the SDLT drive is getting such poor performance?

```
Jun  5 02:45:17 dnn kernel: sa0 at ahc0 bus 0 scbus2 target 6 lun 0
Jun  5 02:45:17 dnn kernel: sa0: <QUANTUM SDLT320 5D5D> Removable Sequential Access SCSI-2 device
Jun  5 02:45:17 dnn kernel: sa0: 40.000MB/s transfers (20.000MHz, offset 8, 16bit)
```


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## Terry_Kennedy (Jun 10, 2012)

monkeyboy said:
			
		

> I recently set up a machine running FreeBSD 8.2 and just tried running a Quantum SDLT drive on an Adaptec 2940W. Using a blocking factor of 50KB, with dump, tar or just dd, I seem to only be getting about 350KB/s. On a similar machine with a DLT drive I get at least 1200KB/s.
> 
> Any clues as to why the SDLT drive is getting such poor performance?


I believe I used -C 32 -b 32 on the dump command line back when I was using a SDLT600 drive. I'm now using a 4MB block size on an LTO drive with a different utility, so I can't test the SDLT options to see if they're optimal.


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## monkeyboy (Aug 16, 2012)

This problem still is unsolved... tried to learn more about it now...

Now I have two systems, #1 running 8.2 AMD64, #2 running 8.3 i386 FreeBSD.

#1 still cannot muster more than 350KB/s on the SDLT 160/320GB drive. This is confirmed with a 2nd SDLT drive. However it does run a DLT1 drive (40/80GB) at 4.8MB/s.

#2 runs both SDLT drives fine, at around 14MB/s, and runs the DLT1 drive at 4MB/s.

Both systems using the same Adaptec 2940W SCSI PCI card. Blocking factors used range from 16KB to 50KB -- it doesn't matter much for the above tests.

I suppose I could try and boot i386 Freebsd on #1 to see if that makes the difference. Otherwise there really is NO difference I can see between #1 and #2...


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## monkeyboy (Aug 17, 2012)

Ok, the problem is mostly resolved...

On a lark, and before going thru the trouble of getting i386 FreeBSD running on system #1, I decide to swap the SCSI controllers, even though they look identical and are both 2940UW's.

Well, after the swap, the problem with slow SDLT transfers on #1 "went away" (no it did not appear on #2). I didn't bother to swap them back, as I was just happy to see up to 24MB/s on #1. Probably some weirdness in the firmware/settings that interacted with the mobo on #1.


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## SirDice (Aug 17, 2012)

Keep in mind 8.2 went End-of-Life at the end of last month. You might want to plan an upgrade to 8.3.


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