[Bug 12481] New: mt takes two minutes to determine that the tape drive is empty

[Bug 12481] New: mt takes two minutes to determine that the tape drive is empty

[bugme-daemon]

http://bugzilla.kernel.org/show_bug.cgi?id=12481

           Summary: mt takes two minutes to determine that the tape drive is
                    empty
           Product: SCSI Drivers
           Version: 2.5
     KernelVersion: 2.6.28
          Platform: All
        OS/Version: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: Other
        AssignedTo: scsi_drivers-other@kernel-bugs.osdl.org
        ReportedBy: kmshanah@ucwb.org.au


Latest working kernel version:
- This definitely used to work fine (no long delays) when we first installed
the tape drive, which was back in July 2007. As we usually keep up to date with
the latest kernels, I assume we were using 2.6.21 at the time but I don't have
any logs to prove it. At the time the kernel was also 32-bit, though I hope
that won't be an important difference.

Earliest failing kernel version:
- Unfortunately, I also have no idea when exactly it broke. It is definitely
broken on at least 2.6.27 and 2.6.28.

Distribution: Debian Lenny (x86_64)
Hardware Environment: Xeon X3350, 8GB RAM, LSI53C1020A, HP LTO-3
Software Environment: mt (GNU cpio 2.9)
Problem Description:
mt is taking two minutes to return the status information for our tape drive
when the drive is empty. It used to be almost immediate. I'm also fairly sure
it used to give a different message as well, something with "OFFLINE" in it,
rather than "rmtopen failed".

Steps to reproduce:
# time mt --file=/dev/nst0 status
mt: /dev/nst0: rmtopen failed: No medium found

real    2m0.709s
user    0m0.003s
sys     0m0.000s


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[Bug 12481] mt takes two minutes to determine that the tape drive is empty

[bugme-daemon]

http://bugzilla.kernel.org/show_bug.cgi?id=12481





------- Comment #1 from kmshanah@ucwb.org.au  2009-01-18 19:54 -------
Created an attachment (id=19882)
 --> (http://bugzilla.kernel.org/attachment.cgi?id=19882&action=view)
Kernel config


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[Bug 12481] mt takes two minutes to determine that the tape drive is empty

[bugme-daemon]

http://bugzilla.kernel.org/show_bug.cgi?id=12481





------- Comment #2 from kai.makisara@kolumbus.fi  2009-01-19 11:10 -------
This is an application bug: it opens the device without the O_NONBLOCK flag.
The driver waits up to two minutes for the drive to become ready. You probably
earlier had an mt that opens tape with O_NONBLOCK (from mt-st?).


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[Bug 12481] mt takes two minutes to determine that the tape drive is empty

[bugme-daemon]

http://bugzilla.kernel.org/show_bug.cgi?id=12481


kmshanah@ucwb.org.au changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |REJECTED
         Resolution|                            |INVALID




------- Comment #3 from kmshanah@ucwb.org.au  2009-01-19 12:37 -------
Thanks, I think you are probably right.
strace shows it (GNU mt) is using open("/dev/nst0", O_RDONLY).

That would also explain why I remember something about the output being
different. I remember now that I had to change my backup script - mt-st outputs
to stdout and shows the status bits of the drive with "DR_OPEN" to indicate the
tape isn't yet loaded, but exits with status 0. GNU mt prints it's error
message to stderr and exits with status 1 when the tape isn't loaded.


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