Re: Problem with scsi tape drives (2.4.18) and soft error count

[Evan Harris]

Only one problem, I'm using devfs, so the major/minor means nothing.  But
from looking at online docs, the normal name for the high bit devices is
nst0, and that just happens to be the device I am using.

But that does explain why the soft error count is always 0 after doing a
tar, since tar closes the device when it's done, and you stated that it
loses all history after that.  A subsequent call to mt would therefore
report 0.

I guess the only way to get the info is to hack a call to retrieve the soft
errors into tar, but I was hoping to avoid that.

Thanks for the info.

Evan

-- 
| Evan Harris - Consultant, Harris Enterprises - [e-mail]
|
| Custom Solutions for your Software, Networking, and Telephony Needs

On Tue, 2 Apr 2002, Richard B. Johnson wrote:

> On Tue, 2 Apr 2002, Evan Harris wrote:
>
> >
> > I've had a long time problem with trying to get the total soft error count
> > from tape devices when using the kernel provided tape interface.
> > Hopefully, someone here can shed some light on the problem.  Using several
> > different DAT and DLT tape drives, the behavior seems the same.
> >
> > I'm trying to figure out how to retrieve the soft error count from a tape
> > drive after having performed a backup.  It helps me to gauge when a tape
> > needs to be retired, and I'm used to being able to get the total soft error
> > count from other backup software packages for dos/windows.
> >
> > mt apparently queries the soft error count, but it always seems to be zero.
> > I've dug into the problem a bit, and it seems that mt reports zero because
> > the tape drive has had it checked and cleared by the kernel at every drive
> > operation.  Is there any place in the kernel that this information is stored
> > so that it may be retrieved?
>
>
> Not really. The soft error count is preserved across the 'correct' kinds
> of open/close operations. To use `mt` to get the count and, to preserve
> the state of the tape machine, you need to do your open/close against
> the minor number that has the high-bit set:
>
> # file /dev/st*
> st0:    character special (9/0)
> st1:    character special (9/1)
> st3:    character special (9/128)
>
> Instead of using /dev/st0, you would use (on this machine) /dev/st3.
>
> So, if you do your I/O and status through /dev/st3, you will get
> meaningful information. Once you close /dev/st0, all history is
> lost (correctly). Note that if you do I/O through /dev/st3, the
> tape will not automatically rewind on close. You will need to
> use `mt` for that.
>
> Cheers,
> Dick Johnson
>
> Penguin : Linux version 2.4.18 on an i686 machine (797.90 BogoMips).
>
>                  Windows-2000/Professional isn't.
>