At 05:11 PM 6-29-98 EDT, Andrew Popay wrote:
>Can anyone tell me if there is a way of enabling the DDS2 & DDS3 drives to
>write in DDS1 format.

The only thing needed to make a DDS-2 or DDS-3 drive write in DDS-1 format
is to use 90m or shorter media.  The higher density formats are only used
on the correspondingly new media formats.

You probably also want to ensure that hardware (really firmware)
compression is disabled when writing types meant to be read on DDS-1
drives.  DDS-2 and later drives all (to my knowledge) support HW
compression.  Early DDS-1 drives do not.  In between were DDS-1 drives
which supported HW compression, often referred to as DDS-DC drives.  If on
MPE 5.0 or later you should be able to use DEVCTRL.PUBXL.TELESUP (at least
I think that's the correct group) to disable and enable compression as
desired.  I suggest that it be done each time you wish to write to tape as
there appear to be several possible events which can switch the tape drive
back to its default mode (probably HW compression enabled).  Trying to read
HW compressed tapes on a drive without HW compression gives media read
errors which look like the tape has failed catastrophically.

You will also want to ensure that all your media to be written in the DDS-2
and later drives incorporate MRS (Media Recognition System), otherwise the
tape will be treated as write-protected by the drive.  DDS-2 and later
media all include MRS.  DDS-1 (90m and shorter) media must have the MRS
logo which is the old stylized "DDS" followed by 4 vertical bars.  Non-MRS
media can be read by DDS-2 and later drives, but can not be written on them
due to the lack of media type information.  (The higher density drives use
the MRS info to know what format in which to write.)
--
Jeff Woods
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