Date: Thu, 27 Mar 1997 13:16:18 -0800 From: Jason Thorpe <thorpej@nas.nasa.gov> To: "David Langford" <langfod@dihelix.com> Cc: arman@bico.co.id, freebsd-hackers@freebsd.org, freebsd-scsi@freebsd.org Subject: Re: DLT exchanger Message-ID: <199703272116.NAA14980@lestat.nas.nasa.gov>
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On Thu, 27 Mar 1997 10:29:59 -1000 (HST) "David Langford" <langfod@dihelix.com> wrote: > The driver works well on the cheapo 4mm Archive/Seagate drive. > The thing that took me awhile to realize was that you had to be very > explicit with chio. You cannot tell it to move a tape into the drive > and expect it to return the one it already has. ...right. This was a concious design decision, which I'll rationalize here: - the driver cannot reasonably keep the state of the changer apparatus; many changers also have front panel controls which may be used at any time by a human operator. - in the case of multiple free slots, who is to make the decision where the in-drive tape should be returned to? This decision is very hard to make, esp. if a human operator has mucked with the front panel controls. - the amount of state one has to keep around gets larger as you add more drives and pickers into the picture. (I've used this with a multi-drive, multi-picker apparatus under NetBSD.) The chio(1) program is meant to be a simple interface for use by scripts/command line. Jason R. Thorpe thorpej@nas.nasa.gov NASA Ames Research Center Home: 408.866.1912 NAS: M/S 258-6 Work: 415.604.0935 Moffett Field, CA 94035 Pager: 415.428.6939
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