Date: Fri, 10 Apr 1998 15:16:33 +0930 From: Greg Lehey <grog@lemis.com> To: "Justin T. Gibbs" <gibbs@narnia.plutotech.com>, FreeBSD current users <FreeBSD-current@FreeBSD.ORG> Cc: FreeBSD-scsi@FreeBSD.ORG Subject: Re: compression on Exabyte 8700LT? Message-ID: <19980410151633.34010@freebie.lemis.com> In-Reply-To: <199804100449.WAA16931@narnia.plutotech.com>; from Justin T. Gibbs on Thu, Apr 09, 1998 at 10:49:14PM -0600 References: <199804091527.QAA09483@albatross.mcc.ac.uk> <199804100449.WAA16931@narnia.plutotech.com>
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On Thu, 9 April 1998 at 22:49:14 -0600, Justin T. Gibbs wrote:
> I don't know why this was sent to questions. It was started on SCSI
> which seems to be where it belongs...
I saw it on -scsi and -questions. Since it related to -current, I
followed up there. The copy to -questions was a one-off to tell
people where it had gone.
>> -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.
>
> Neither the old driver, nor the CAM driver performs any type of guessing
> about the size of the tape.
I didn't think so. I was just wondering why the capacity was so much
less than the nominal capacity.
>> 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?
>
> The decision was that it should return ENOSPC. The CAM driver does
> return ENOSPC. I have patches, in my CAM tree, to ensure that dump
> and restore correctly deal with ENOSPC as an EOT condition.
Good.
> Someone should probably check pax, cpio, and tar.
I'll definitely check tar.
>> Would I get an improvement on either of these points if I installed
>> CAM?
>
> Probably. You may want to wait for the weekend though. I'm "this close"
> to finishing the BusLogic driver, and I intend to release a new snapshot
> at that time. This will also include some improvements to the tape
> driver.
Good. I'll do that. Is it now in -CURRENT?
>> I know that CAM can't handle compression switching yet, but can
>> it do compression if it's enabled on the drive?
>
> The next snapshot will have compression and density control support.
> Ken's already implemented, and tested it.
Great
Greg
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