[nycbug-talk] tape drive woes

[Tillman Hodgson]

On Thu, Feb 03, 2005 at 07:46:48PM -0500, Dan Langille wrote:
> I was given a DDS-4 tape drive at BSDCan last May.  Last night, it 
> started acting up.
> 
> The following gives the following:
> 
>    mt -f /dev/sa0 status => http://www.langille.org/tmp/ach-dumps.txt

I get that (SCSI bus resets) with my DDS-1 and -2 drives as well and
I've seen it with DDS-3 drives.

> It's not the card (I hooked up a SCSI disk and newfs'd it, just 
> fine).  It's not the cable (I tried another one, but not a new one).

Right. In my case, different cards and cables didn't help. A new tape
(as in brand new) helped, sometimes, for a short time.

I suspect that the drive needs cleaning. DDS drives need cleaning like a
baby needs changing. I typically run a cleaner tape through after 2 tape
runs now and I *still* encounter those errors, though at a significantly
reduced rate.

Putting the drive on it's on SCSI controller helps, because when it
/does/ happen it doesn't freak out all the other devices on the bus.

The traditional wisdom with bus resets is that it's due to exceeding the
SCSI specifications in some manner: poor termination, too-long cable,
that sort of thing. I've have luck with a DEC StorageWorks JBOD tower
that used to bus reset like a mad banshee simply by telling the
controller to run it at a slower rate -- a more robust SCSI bus results
from the "easier" specifications. Since this particular SCSI controller
only "auto-detects" SCSI settings and won't allow me override them in
it's "BIOS", I wrote a /etc/rc.d script that manually forces the devices
down one speed notch just before fsck kicks in (which would cause bus
resets like crazy). The basic idea is this:

  camcontrol negotiate da0 -R10 -q -a

I'm simply moving the bus from 20MHz to 10MHz which, at 16 bits wide,
moves me from 40MB/s to 20MB/s. That's more than fast enough for the
drives I have in the JBOD (which aren't ever accessed simultaneously
with the use I've put them to) and all top out at about 12MB/s anyway).

It's worth a try, especially considering that DDS-4 doesn't write fast
enough to need the full 40MB/s of Ultrawide SCSI.

> So I'm looking at buying a Seagate DDS-4 Scorpion STD2401LW 
> <http://tinyurl.com/5g6ga> for CAD$650 (+taxes).
> 
> Anyone got one and can tell stories about it?

No, but I also had no idea that they'd gotten so cheap. *Damn*, that's
tempting :-)

> Please note: This is not the thread for saying tape is crap, DAT is 
> crap, use HDD, use DLT, etc... Unless of course, you're prepared to 
> give me the hardware and the media. Then I'm prepared to listen.  :)

And if anyone is handing out tape hardware, I'm willing to cover the
cost of shipping if it's to help out freshports.org.

-T


-- 
Fsck, either way I'm screwed. -- petro
Now *that* is the Sysadmin's motto. -- Peter da Silva