We are using SunOS 4.1.1 so I dunno if 4.1.2 recognizes it automatically
or not. Unfortunately I've lost the performance test I did when we installed
it some time ago. The information I have says that with the patches
below applied (but with a smaller number, 5000 instead of 10240) it will
"allow for a transfer rate of 8-11MB/minute, whereas with the
default settings, transfer rates will not exceed 3-4MB/min". In my experience
the difference will be even greater since without the patches the
drive did not stream well... On our system I think it backs up a
700MB (almost full) partition in one hour using SMD-E disks and using
"dump" (it was a while since I last "timed" a full backup...)

I like the HP DAT a lot. It's really easy to use and we've so far
had no problems with tapes or anything (we're reusing the DDS tapes).
And the tapes are so small that it's really easy to store/transport them.

Ok, here are the changes we did for our Sun 4/380. This is for
a "sun4" architecture. Which we are using. I've also included some
information I have for adding the drive to a "sun4c" architecture. 
(I haven't tested that myself, since i haven't got access to a
"sun4c" machine).

Also note that our changes are for the HP 35450A DDS drive (1.3GB).
(You'll probably be able to use the same code for other HP DDS drives,
just by changing the drive ID..)

You can change the "10240" number below up/down to getter better/worse
performance. The information I have says that "10240 = 512 * 20, and that
it may be changed up to the 5K limit of the drive". I suppose that
means that the 512 number may be increased up to 5120, but I don't know
for sure.

If you try it out and find the optimal number I'd be very happy if
you could tell me (I'm having a little problem testing it myself
since the machine the DDS drive is sitting in is our main server
and users tend to be somewhat irritated when the machine goes into
yo-yo mode while I'm testing.. :-)

If you have a "sun4" architecture (with the "old scsi") do this:

1. Edit /sys/sundev/streg.h and add in the "ST_TYPE_*" #define list an
   entry like:

      #define ST_TYPE_HPDAT        0x29

2. Then below in the "ST_DRIVE_INFO" macro add last after the
   entry for the "Fujitsu 3480 1/2":

  {	"HP-35450A 4mm DAT", 2, "HP", ST_TYPE_HPDAT, 10240, \
	(ST_VARIABLE | ST_BSF | ST_BSR | ST_LONG_ERASE | ST_AUTODEN_OVERRIDE),\
	17, 17, 17, 17,	6, 6, 6, 6, \
        0x00, 0x00, 0x00, 0x00 , 0, 0, 0, 0 }, \

3. "Reconfig" and rebuild your kernel. Then boot the machine with the
    new kernel.

******************** End of changes needed for "sun4" ********************

Below follows the information I have about adding a HP DDS drive to a
"sun4c" architecture kernel (with the "new scsi"):

1. Edit /sys/scsi/targets/stdef.h and add after the #define for
   ST_TYPE_EXABYTE this:

   #define ST_TYPE_HPDAT     0x29

2. Then edit /sys/scsi/targets/st_conf.c and add after the
   "Exabyte 8mm Helical Scan" entry either one of the following
   (The first one is probably better since it won't be that
   sensitive to name changes...):

2a:
   /* HP 4mm Helical Scan */
   {
	"HP-35450A 4mm DAT", 2, "HP", ST_TYPE_HPDAT, 1024,
        (ST_VARIABLE | ST_BSF | ST_BSR | ST_LONG_ERASE | ST_AUTODEN_OVERRIDE),
        10240, 10240,
        { 0x00, 0x00, 0x00, 0x00 },
        { 0, 0, 0, 0}
   }

2b:
   /* HP DAT 4mm cartridge */
   {
 	"HP DAT", 24, "HP      HP35450A      -A",
        ST_TYPE_HPDAT, 10240,
        (ST_VARIABLE | ST_BSF | ST_BSR | ST_LONG_ERASE | ST_AUTODEN_OVERRIDE),
        10240, 10240,
        { 0x00, 0x00, 0x00, 0x00 },
        { 0, 0, 0, 0}
   }        

3. "Reconfig" and rebuild your kernel. Then boot the machine with the
    new kernel.

/Peter