From mboxrd@z Thu Jan 1 00:00:00 1970 From: pechter@gmail.com (William Pechter) Date: Mon, 20 Nov 2017 18:35:25 -0500 Subject: [TUHS] Determining what was on a tape back in the day In-Reply-To: References: <20171119134109.59F3018C0F5@mercury.lcs.mit.edu> <7AA20D14-571A-4AAD-96D0-45057F5B81DD@jctaylor.com> <1CE2C7FC-1FAE-44F7-8DDA-B21D54FA0E43@ronnatalie.com> <1511201558.524826.1178671936.79EC560B@webmail.messagingengine.com> Message-ID: <3a7416ad-b695-77bc-92c3-d37e6fddccc1@gmail.com> Dave Horsfall wrote: > On Mon, 20 Nov 2017, Random832 wrote: > >> For whatever it's worth, the tm(4) and ht(4) manpages from V5 onward >> say "seeks have their usual meaning", and both drivers provide a >> 'non-raw' device which is a block device and (according to the >> manual) only supports tapes consisting of 512-byte records - the BUGS >> section mentions that the raw device, conversely, does *not* support >> seeking. > > Thank you; I dimly recall that seeks were implemented by the driver > keeping track of whichever block was under the head, and skipping > forwards or backwards accordingly, with simple arithmetic. I no longer > have access to those sources, but we at UNSW certainly modified Unix > rather heavily, so if that capability is not in the distributed > version then it means that we modified it; this was over 30 years ago... > > It bloody well worked as a read-only file system; I take great umbrage > at the implication that I am a liar, and I'm the sort of obstreperous > bastard who neither forgives not forgets... > I know that a read-only filesystem for installs is possible.  Pyramid Technologies used a tape install filesystem called ROFS...guess what that stands for... We used it on both cartridge (QIC-150 iirc) and 9 track magtapes... So there's no special type of drive needed. It was created by dd-ing  a chrooted specially constructed file tree (IIRC).   I constructed special ones at my site with all the site specific info (passwords, groups, etc) on it for emergency recovery. It was used for their OS/x (BSD-SysV dual universe for their Risc CPU) and DCOSx (SVR4 port to Mips R3000). Bill