Date: Tue, 5 Sep 2000 08:56:50 +0200 From: Martin Cracauer <cracauer@cons.org> To: Chris Dillon <cdillon@wolves.k12.mo.us> Cc: Christian Weisgerber <naddy@mips.inka.de>, freebsd-scsi@FreeBSD.ORG Subject: Re: Keeping a DLT4000 streaming? Message-ID: <20000905085650.A37471@cons.org> In-Reply-To: <Pine.BSF.4.21.0009031400140.90484-100000@mail.wolves.k12.mo.us>; from cdillon@wolves.k12.mo.us on Sun, Sep 03, 2000 at 02:19:30PM -0500 References: <8oth09$u2b$1@ganerc.mips.inka.de> <Pine.BSF.4.21.0009031400140.90484-100000@mail.wolves.k12.mo.us>
next in thread | previous in thread | raw e-mail | index | archive | help
In <Pine.BSF.4.21.0009031400140.90484-100000@mail.wolves.k12.mo.us>, 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 <cracauer@cons.org> 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
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20000905085650.A37471>