Messages in this thread | | | Date | Tue, 2 Apr 2002 16:01:56 -0500 (EST) | From | "Richard B. Johnson" <> | Subject | Re: Problem with scsi tape drives (2.4.18) and soft error count (BusLogic, AIC7xxx) |
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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.
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