Date: Fri, 25 Oct 1996 09:30:17 +0200 (MET DST) From: J Wunsch <j@uriah.heep.sax.de> To: freebsd-hackers@freebsd.org (FreeBSD hackers) Cc: pst@jnx.com (Paul Traina) Subject: Re: SCSI tape drive density codes and block sizes...? Message-ID: <199610250730.JAA07964@uriah.heep.sax.de> In-Reply-To: <199610250109.SAA04642@base.jnx.com> from Paul Traina at "Oct 24, 96 06:09:25 pm"
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As Paul Traina wrote: > What exactly do the density codes for my DDS2 (HP C1533A) tape drive mean? > What density code do I want to be using? > > Present Mode: Density = 0x24 Blocksize variable The tape density modes that are known to mt(1) by name are those mentioned in the SCSI-2 specs. Since these specs are a little aging these days, most modern drives needed additional mode values. You normally don't want to change it. I think the driver should normally not even try to handle them at all, but always use the default density and blocksize. However, right now the driver insists on always setting density and blocksize. Half of our tape-drive related `quirk' records would probably not really needed. Things are a little different if you've for example got a QIC-24 (60 MB) cartridge in a QIC drive that would be misdetected as QIC-150, you want to override the density value in this case for proper operation. For DDS drives with the ``media recognition system'', the cassettes are supposed to be detected properly. Some HP guy told me that DOS software often uses fixed-length records even for DAT. So if you encounter such a tape, you might want to adjust your tape driver, too. Unixoides normally use variable-length records however (wherever supported by the hardware, i.e. with QIC >= 525, DAT, Exabyte 8 mm etc.), so that's the default for these drives. -- cheers, J"org joerg_wunsch@uriah.heep.sax.de -- http://www.sax.de/~joerg/ -- NIC: JW11-RIPE Never trust an operating system you don't have sources for. ;-)
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