From owner-freebsd-questions Thu Apr 9 18:54:56 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id SAA25829 for freebsd-questions-outgoing; Thu, 9 Apr 1998 18:54:56 -0700 (PDT) (envelope-from owner-freebsd-questions@FreeBSD.ORG) Received: from allegro.lemis.com (allegro.lemis.com [192.109.197.134]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id SAA25594; Thu, 9 Apr 1998 18:54:21 -0700 (PDT) (envelope-from grog@lemis.com) Received: from freebie.lemis.com (freebie.lemis.com [192.109.197.137]) by allegro.lemis.com (8.8.7/8.8.5) with ESMTP id LAA16680; Fri, 10 Apr 1998 11:24:09 +0930 (CST) Received: (from grog@localhost) by freebie.lemis.com (8.8.8/8.8.7) id LAA00741; Fri, 10 Apr 1998 11:24:08 +0930 (CST) (envelope-from grog) Message-ID: <19980410112408.01873@freebie.lemis.com> Date: Fri, 10 Apr 1998 11:24:08 +0930 From: Greg Lehey To: ip@mcc.ac.uk, questions@FreeBSD.ORG, scsi@FreeBSD.ORG, FreeBSD current users Subject: Re: compression on Exabyte 8700LT? Reply-To: FreeBSD current users References: <199804091527.QAA09483@albatross.mcc.ac.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 0.89i In-Reply-To: <199804091527.QAA09483@albatross.mcc.ac.uk>; from Ian Pallfreeman on Thu, Apr 09, 1998 at 04:27:31PM +0100 WWW-Home-Page: http://www.lemis.com/~grog Organization: LEMIS, PO Box 460, Echunga SA 5153, Australia Phone: +61-8-8388-8286 Fax: +61-8-8388-8725 Mobile: +61-41-739-7062 Sender: owner-freebsd-questions@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG On Thu, 9 April 1998 at 16:27:31 +0100, Ian Pallfreeman wrote: > I've recently acquired another Exabyte drive, an 8700LT. This drive claims to > be able to write 10Gb to a 112m tape in compressed mode, but I'm getting just > the 5Gb I'd expect uncompressed. > > ... > > FreeBSD 3.0-CURRENT #9: Thu Apr 9 16:06:09 BST 1998 > ip@lurch:/usr/src/sys/compile/LURCH Please don't discuss CURRENT topics on -questions. Send them to -current instead (to which I hope you are subscribed). I'm copying -questions on this reply only to show where I've sent the thread. I think there's a general problem with tape compression under -CURRENT. A few months back, I used to be able to back up a complete 8 GB on my DDS-2 drives, but now I've done some testing and found it gives up somewhere round 3.4 GB. I don't understand that, since the native tape capacity is 4 GB. -CURRENT people: I'm using the old SCSI driver. The tape is set to start up in compressed mode, and the DC LED is illuminated all the time. This looks to me as if something in the driver is explicitly disabling compression, or just possibly that the driver is guessing the size of the tape and stopping (with EIO) when it reaches this point. The other point is that it's still returning EIO. I know there's been some discussion about this before, and ISTR that it was inconclusive ("that's the way our grandfathers did it"). While looking at the problem, I came across a program I wrote in my BSD/OS days back in 1992, and I note that even then BSD/OS returned ENOSPC when it got to the end of the tape. This makes a whole lot more sense, and it obviously seems to have withstood the test of time. How about it? Would I get an improvement on either of these points if I installed CAM? I know that CAM can't handle compression switching yet, but can it do compression if it's enabled on the drive? Greg To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-questions" in the body of the message