SUMMARY: DLT-2000 (TZ87) performance problem

From: Nate Itkin (
Date: Wed Jan 25 1995 - 19:04:03 CST

Once again, the sun managers list has delivered.

The following tape drive gurus have my sincere thanks:

        Rich Schultz (
        Harry Edmon (
        Scott Stubbs (
        David Warm (
        Sydney S. Weinstein, CDP, CCP (syd@Myxa.COM)
        Larry Kelley (
        Jerry Ratner (

My original question involved poor performance of DLT drives during
a space over filemarks operation.

It was nearly unanimous that the solution was to add ST_KNOWS_EOD as an
option in the st_conf.c entry. In doing so, the time required for a
large file space operation (mt -f /dev/dlt fsf x) was reduced from 30
minutes to 2 minutes. This is still 30 seconds longer than the spec.
called out in the DLT-2000 product manual, but it's certainly acceptable.

The winning entry for st_conf.c:

        /* DEC DLT-2000 */
                "DEC DLT2000", 3, "DEC", ST_TYPE_REEL, 16384,
                ( ST_REEL | ST_VARIABLE | ST_BSF | ST_BSR | ST_KNOWS_EOD ),
                400, 400,
                { 0x17, 0x18, 0x19, 0x19 },
                { 0, 0, 0, 0 },

I should also be noted that two persons suggested that it was a density
select problem and { 0x17, 0x18, 0x19, 0x19 } should be changed to
{0x81, 0x80, 0x18, 0x17}. According to the DLT-2000 product manual, the
density select values are:

        0x16 - 10000 bpi MFM serial cart. tape X3.193-1990 (read only)
        0x17 - 42500 bpi MFM serial cart. tape X3B5/91-174 - 2.6 GB
        0x18 - (same as 0x17 but with 56 track pairs .vs 24) - 6.0 GB
        0x19 - 62500 bpi, 64 track pairs, serial cart. tape - 10 GB

It's unclear to me exactly what magic voodoo occurs with a density select of
0x80 or 0x81, but doing so allegedly solves the problem. I did not take
time to test this. If someone would care to explain it, I will gladly
follow up with an enhanced summary.

- Nate Itkin
- Portland Technology Development, Intel Corporation      Aloha, Oregon
- E-mail:

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