Date: Fri, 10 Apr 1998 11:24:08 +0930 From: Greg Lehey <grog@lemis.com> To: ip@mcc.ac.uk, questions@FreeBSD.ORG, scsi@FreeBSD.ORG, FreeBSD current users <FreeBSD-current@FreeBSD.ORG> Subject: Re: compression on Exabyte 8700LT? Message-ID: <19980410112408.01873@freebie.lemis.com> In-Reply-To: <199804091527.QAA09483@albatross.mcc.ac.uk>; from Ian Pallfreeman on Thu, Apr 09, 1998 at 04:27:31PM %2B0100 References: <199804091527.QAA09483@albatross.mcc.ac.uk>
next in thread | previous in thread | raw e-mail | index | archive | help
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-current" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?19980410112408.01873>