From owner-freebsd-scsi Mon Sep 4 23:57:41 2000 Delivered-To: freebsd-scsi@freebsd.org Received: from gilgamesch.bik-gmbh.de (T1-Hansenet.BIK-GmbH.de [192.76.134.246]) by hub.freebsd.org (Postfix) with ESMTP id A6ED937B422 for ; Mon, 4 Sep 2000 23:57:36 -0700 (PDT) Received: (from cracauer@localhost) by gilgamesch.bik-gmbh.de (8.9.3/8.7.3) id IAA38241; Tue, 5 Sep 2000 08:56:50 +0200 (MET DST) Date: Tue, 5 Sep 2000 08:56:50 +0200 From: Martin Cracauer To: Chris Dillon Cc: Christian Weisgerber , freebsd-scsi@FreeBSD.ORG Subject: Re: Keeping a DLT4000 streaming? Message-ID: <20000905085650.A37471@cons.org> References: <8oth09$u2b$1@ganerc.mips.inka.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Mailer: Mutt 1.0.1i In-Reply-To: ; from cdillon@wolves.k12.mo.us on Sun, Sep 03, 2000 at 02:19:30PM -0500 Sender: owner-freebsd-scsi@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.org In , Chris Dillon wrote: > On 3 Sep 2000, Christian Weisgerber wrote: > > > If any of you guys have a DLT4000 (or faster) tape drive, and > > manage to keep it streaming properly _with compression enabled_, > > I'd like to know your setup. > > Keeping a DLT4000 streaming would be a lot harder than keeping a > DDS2/3 drive streaming, but I keep my DDS drive streaming (with no H/W > compression, I have to use gzip instead) by using several large 'team' > (ports/misc/team) buffers. I currently use five 8MB buffers. A > buffer only empties when it is full, so that way only 8MB streamable > chunks make it to the drive, even if the disks can't keep all of the > buffers full. You might want 32MB at a time or more for a DLT drive > that is doing its own compression. I believe I had to modify the team > code to get even an 8MB buffer. I wrote ports/misc/cstream partly for this purpose. Using -B and -c you get buffering without size restrictions. Some of the -c modes are - while being well-tested - experimental, so be sure to check results if you want to use it for backup purposes. cstream also has data sinks and generators for quasi-random ascii data which would be useful to isolate the problem. Feedback welcome, of course. While we are at it, I'm having a different problem with my DTL. It writes 2.4 -3.0 MB/sec at 32kb blocksize, but it reads only 1 MB/sec. At smaller blocksizes I get get both reading and writing at 1.5 MB/sec. These tests are done with without using the filesystem, just one userspace program. Any idea what could make reading slower than writing? Martin -- %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Martin Cracauer http://www.cons.org/cracauer/ BSD User Group Hamburg, Germany http://www.bsdhh.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message