exabyte errors

[Lisa Amedeo]

     Mark Bartlet writes:

     Finally, question #3.  Does anyone have a clue as to what's going on here?

  % maketape /dev/rmt/tps0d7nsv         # "nsv" device works fine
  5+0 records in
  5+0 records out
  10+0 records in
  10+0 records out
  15+0 records in
  15+0 records out
  % 
  % maketape /dev/rmt/tps0d7ns          # "ns" device doesn't
  5+0 records in
  5+0 records out
  dd: write error: I/O error
  3+0 records in
  3+0 records out
  dd: write error: I/O error
  3+0 records in
  3+0 records out
  % 

     I think the problem lies in the fact that Mark has changed devices
     from variable to fixed (i.e. tps0d7nsv to tps0d7ns).

     After much investigation by serveral people at FERMI and at SGI, it
     turns out that in 3.3.1 and 3.3.2 of IRIX, there is a problem that
     occurs when moving between the variable length 8mm device ( tps*v)
     and the fixed devices.  The problem is as follows:  upon bootup,
     all devices work as they should and each device has a default block
     size variable set.  The fixed device block size should be 1024.

     Now lets say you use a variable device for *any* command that accesses
     the tape drive (this includes mt).  The correct default block size is
     set and things work fine until you try to switch back to the fixed
     device.  The move from variable to fixed resets the block size and now
     the fixed device has a block size of one (1). Remember it should be 
     1024.   Meaning, when you try to write to the tape, the tape protocol
     looks at the default block size and says that one byte of data will
     be written to a 1024 byte block.  Then the rest of the block will
     be filled with filler.  Technically this should work, even if it does
     take forever, however the exabyte drive times out.  

     The only way to fix this problem is to reboot the system or compile
     the program below and run it prior to any usage of a fixed device. 
     This program was given to us by SGI reps working on this issue.  


     I believe this problem is seperate from the scsi failures others have
     seen.  I have also seen the scsi errors in SYSLOG since upgrading to
     3.3.2 and the errors have occured on systems that are using the 
     8mm variable device exclusively.  On one of the systems with the
     scsi failures, I shutdown, reseated all connectors then came back up.
     The scsi failures have not been recorded since then ( about two weeks 
     ago ).
     
     Hope this solves some of the exabyte trouble others have been having!     
     And by the way, SGI says the fixed block size problem will be gone in
     4.0 of IRIX.


                                                  Lisa Amedeo
                                           UNIX System Administrator 
                                      FERMI National Accelerator Laboratory
                                               Batavia, Illinois
                                                 (708) 840-8023 
                                       e-mail: amedeo at dcdlaa.fnal.gov

-------%<---------------%<-----------------%<------------------%<--------------


/*   C program to fix the 8mm exabyte fixed device block size.               */
/*      This program is duplicated here exactly as it was given to us by     */
/*      SGI technical REPS.  Note that the program hard codes the tape       */
/*      device in as /dev/tape.  By SGI default, /dev/tape accesses tape     */
/*      device /dev/mt/tps0d2.  If you are using a different device you      */
/*      will need to change the appropriate line in the code.                */



#include <sys/types.h>
#include <sys/mtio.h>
#include <stdio.h>

main()
{
        struct mtop mtop;
        int fd;

        if((fd=open("/dev/tape", 0)) == -1) {
                perror("tape open failed");
                exit(1);
        }
        mtop.mt_op = MTSCSI_SETFIXED;
        mtop.mt_count = 1024;   /* exabyte default fixed block size */
        if (ioctl(fd, MTSPECOP, &mtop) < 0) {
                fprintf(stderr, "setblksize ioctl on %s ");
                perror("failed");
                exit(2);
        }
        exit(0);
}