Date: Mon, 29 Jan 1996 12:06:56 -0800 From: Darryl Okahata <darrylo@hpnmhjw.sr.hp.com> To: Ollivier Robert <roberto@keltia.freenix.fr> Cc: joerg_wunsch@uriah.heep.sax.de, freebsd-scsi@freebsd.org Subject: Re: mt Message-ID: <199601292006.AA001896016@hpnmhjw.sr.hp.com> In-Reply-To: Your message of "Mon, 29 Jan 1996 08:48:32 %2B0100." <199601290748.IAA01157@keltia.freenix.fr>
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> I think there is a jumper to enable/disable compression but:
> - it is not written in the doc :-(
> - I'd rather have a software switch.
[ Note: while I work for HP, I have nothing to do with DAT drives,
printers, or calculators, except for using them. ]
A software switch does exist. There's an HP-internal document that
does describe the swtich settings, and I'm trying to get permission to
send them to you (there is apparently *NO* simple one-to-one mapping of
switch settings and drive features).
When configured for use with Sun workstations (and possibly
others?), the HP DAT drives supposedly ignore mode select (I can't tell
if the drive completely ignores mode select, or if the drive simply
ignores the mode select command that turns off the drive's buffer).
Possible switch settings include (where the drive ignores mode select):
1 2 3 4 5 6 7 8 <-- Switch number
1 1 1 1 1 0 0 0 <-- One possible switch setting (MRS off)
1 1 1 1 1 0 0 1 <-- Another possible switch setting (MRS on)
Instead, you might want to try using an "HP workstation" switch setting:
1 2 3 4 5 6 7 8 <-- Switch number
1 1 0 1 1 1 1 1 <-- One possible switch setting (MRS on)
This setting assumes that FreeBSD is not writing lots of non-immediate
filemarks and not disabling buffering (there's another setting to make
the drive stream for this case). This setting also enables the "Media
Recognition System" (MRS), where you must put a DDS-grade DAT tape into
the drive (non-DDS-grade tapes are treated as read-only tapes). If you
want to disable MRS, try using:
1 2 3 4 5 6 7 8 <-- Switch number
1 1 1 1 1 1 1 1 <-- One possible switch setting (MRS off)
Please note that I haven't tested these settings, but I believe they
will work.
-- Darryl Okahata
Internet: darrylo@sr.hp.com
DISCLAIMER: this message is the author's personal opinion and does not
constitute the support, opinion, or policy of Hewlett-Packard, or of the
little green men that have been following him all day.
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