From owner-freebsd-hackers Sat Aug 15 13:24:02 1998 Return-Path: Received: (from majordom@localhost) by hub.freebsd.org (8.8.8/8.8.8) id NAA06334 for freebsd-hackers-outgoing; Sat, 15 Aug 1998 13:24:02 -0700 (PDT) (envelope-from owner-freebsd-hackers@FreeBSD.ORG) Received: from smtp03.primenet.com (smtp03.primenet.com [206.165.6.133]) by hub.freebsd.org (8.8.8/8.8.8) with ESMTP id NAA06329 for ; Sat, 15 Aug 1998 13:24:01 -0700 (PDT) (envelope-from tlambert@usr01.primenet.com) Received: (from daemon@localhost) by smtp03.primenet.com (8.8.8/8.8.8) id NAA28913; Sat, 15 Aug 1998 13:23:31 -0700 (MST) Received: from usr01.primenet.com(206.165.6.201) via SMTP by smtp03.primenet.com, id smtpd028877; Sat Aug 15 13:23:22 1998 Received: (from tlambert@localhost) by usr01.primenet.com (8.8.5/8.8.5) id NAA20511; Sat, 15 Aug 1998 13:23:15 -0700 (MST) From: Terry Lambert Message-Id: <199808152023.NAA20511@usr01.primenet.com> Subject: Re: TESTERS WANTED for new ATAPI CD/CDR/CDRW driver. To: mike@smith.net.au (Mike Smith) Date: Sat, 15 Aug 1998 20:23:15 +0000 (GMT) Cc: thorpej@nas.nasa.gov, hackers@FreeBSD.ORG In-Reply-To: <199808151153.LAA01317@word.smith.net.au> from "Mike Smith" at Aug 15, 98 11:53:23 am X-Mailer: ELM [version 2.4 PL25] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG > I'd be curious to know if anyone's measured the cost of the SCSI<->ATA > translation for ATA disks, since that's where performance is really an > issue. Nobody cares how efficient access to a Zip disk is, but an > extra 10% overhead on ATA disk transactions would really hurt. > > Command passthrough doesn't (can't) work directly, as many fields are > different sizes. I think what you mean is that there's no need for any > intelligence in the translation, which is fair enough. A question I have is this: If I'm passing SCSI commands down, is it possible to actually support multiple outstanding tagged commands? I know that the EIDE specification allows for this, but I am unaware of any IDE disk drives that support it. If I could get multiple outstanding transactions at a cost of 10% overhead, all I need is two of them and my system is running 80% faster than it was... For a single user workstation running a curses program on the console, this is not a problem. For any other load, this should generally be a win, especially if swapping is occurring. The inability of most IDE hardware to support multiple outstanding tagged commands is the primary reason I still recommend SCSI to people who are running light loads and are never going to need more than one disk and one CDROM (though "never" is a very long time indeed... for systems with most Intel chipsets, there is a limit to 2 simultaneous PCI bus masters before the negotiation fails, meaning I'm limited to 4 IDE devices no matter what). Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message