SUMMARY: 4mm DAT parameters

From: John Horne (
Date: Mon Mar 23 1998 - 05:05:49 CST

Original question:
> We have used 4mm DAT's for some time now and were originally told by Sun
> (UK)
> to use:
> dump 0udsf 61000 5000 ...
> No blocking factor was specified. Can anyone enlighten me as to what the
> parameters *should* be? We currently use both 60m and 90m tapes if that
> makes a difference. Any help DLT IV's as well could be useful :-)
Thanks to all those whole replied. Unfortunately there doesn't seem to be a
definitive answer. Two people sent me a copy of the Sunos 4.1.4 document (see
below); one other user stated that they used a blocking factor of 126 with no
problems (DLT as well).

I am of the opinion that the size value is irrelevant as the tape unit can
detect the end of tape. As for blocking factor and density, well...we use
96 and 61000 with no problems; but others use other values with no problems

Here is a copy of a file that I downloaded from Sun is the US. Here

Symptoms and Resolutions article 10688
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SRDB ID: 10688

SYNOPSIS: Dump parameters for 4mm dat


What are the dump parameters for 4mm DAT drive for 4.1.3U1?


Here are the dump parameters for 4.1.3U1.

Native (non-compressed) mode:

  dump 0ubdsf 96 54000 5200 /dev/rst0 /dev/xxx

     The 96 specifies a blocking factor of 48 which is optimum for
     The 54,000 is the same density factor used for the 8mm drives
     The 5,200 is used for size instead of 6000, because the DAT has a
     capacity of 2GB rather than the 2.3GB capacity of 8mm drives.
     The rst0 specifies non compression mode (this is very important)

compression mode:

    The DAT drive supports compression. However, it is not possible to
    determine how much data will fit on a tape. A typical value is
    non-compression mode, but in some cases the data won't fit on the
    tape and in many cases the data is muchmore compressible and tape
    capacity will be wasted.

    To be on the safe side, doubling the capacity is recommended. It
    be noted however that in some cases even this may not be
    enough, and that the only way to guarantee that the dump will not
    out of tape is to not use compression.

    Doubling the size option (5200 in non-compressed mode) results in
    following command:

        dump 0ubdsf 96 54000 10400 /dev/rst8 /dev/xxx

   The 10400 specifies an anticipated capacity of 4Gbytes. Note the
   use of /dev/rst8 instead of /dev/rst0.

PRODUCT AREA: System Administration
PRODUCT: Device config

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