Date: Mon, 20 Dec 1999 23:59:56 -0800 (PST) From: "Rodney W. Grimes" <freebsd@gndrsh.dnsmgr.net> To: mjacob@feral.com Cc: freebsd-arch@freebsd.org, syssgm@detir.qld.gov.au (Stephen McKay), grog@lemis.com (Greg Lehey), rb@gid.co.uk (Bob Bishop), rivers@dignus.com (Thomas David Rivers), joerg_wunsch@uriah.heep.sax.de (Joerg Wunsch), hf@Melog.DE (Hauke Fath) Subject: Re: filemarks? Message-ID: <199912210759.XAA45289@gndrsh.dnsmgr.net> In-Reply-To: <Pine.BSF.4.10.9912202333570.56276-100000@beppo.feral.com> from Matthew Jacob at "Dec 20, 1999 11:51:18 pm"
next in thread | previous in thread | raw e-mail | index | archive | help
... > Write Behaviour near End of Media > > A user application detects EARLY WARNING during writing by > getting a return from the write(2) system call of zero ... [My model deleted along with lots of other stuff] > > > > Whats wrong with this model? > > The user application cannot distinguish EARLY WARNING from hard EOT directly. > You can put more data on tape after EARLY WARNING and before hard EOT. Trying to put any more data on tape after EARLY WARNING will make your tapes _extreamly_ non-portable. Infact doing anthing more than either writting filemarks, or bsr and filemarks will make your tape(s) unreadable on most systems out there. I think this is covered in one of the ANSI specs, but can't find a reference handy :-(. I do know from first hand work with things like VMS Backup that the SOP on early warning is, bsr, weof, weof, rewind. And in every tape application I have ever worked on that handled multivolumes on just about any tape drive accross any system this was what _had_ to happen to make it work, independent of tape drive type (9-track, mega-tape, QIC, 8mm, dat). Only applications intimately familiar with the tape drive they are working with should ever try to count on data being correct past Early Warning, independent of if you are reading or writing. -- Rod Grimes - KD7CAX @ CN85sl - (RWG25) rgrimes@gndrsh.dnsmgr.net To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199912210759.XAA45289>