From owner-freebsd-hackers@FreeBSD.ORG Wed Dec 7 21:51:04 2005 Return-Path: X-Original-To: hackers@freebsd.org Delivered-To: freebsd-hackers@FreeBSD.ORG Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 444A816A42B for ; Wed, 7 Dec 2005 21:51:04 +0000 (GMT) (envelope-from anderson@centtech.com) Received: from mh1.centtech.com (moat3.centtech.com [207.200.51.50]) by mx1.FreeBSD.org (Postfix) with ESMTP id 66ADA43D73 for ; Wed, 7 Dec 2005 21:51:02 +0000 (GMT) (envelope-from anderson@centtech.com) Received: from [10.177.171.220] (neutrino.centtech.com [10.177.171.220]) by mh1.centtech.com (8.13.1/8.13.1) with ESMTP id jB7Lox0J001845; Wed, 7 Dec 2005 15:51:00 -0600 (CST) (envelope-from anderson@centtech.com) Message-ID: <43975926.1010302@centtech.com> Date: Wed, 07 Dec 2005 15:50:30 -0600 From: Eric Anderson User-Agent: Mozilla Thunderbird 1.0.7 (X11/20051204) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Nate Lawson References: <4395BF04.50101@centtech.com> <43960F55.3010508@root.org> In-Reply-To: <43960F55.3010508@root.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Virus-Scanned: ClamAV 0.82/1205/Wed Dec 7 08:00:48 2005 on mh1.centtech.com X-Virus-Status: Clean Cc: hackers@freebsd.org Subject: Re: scsi-target and the buffer cache X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 07 Dec 2005 21:51:04 -0000 Nate Lawson wrote: > Eric Anderson wrote: > >> I'm curious about whether a target mode device would use the buffer >> cache or not. Here's a scenario: >> >> Host A: has fibre channel host adapter, in target mode, large memory >> pool, and another fiber channel host adapter connecting to fibre >> channel block device. >> Host B: Fibre channel host adapter, connecting to Host A. 'sees' the >> target mode block device created by Host A. >> >> Will Host A use the buffer cache to cache blocks between the real >> block device, and the shared target mode device? >> What about if Host A put a filesystem on the block device, created a >> single file the size of the filesystem, and shared that filesystem >> via a target mode device to Host B? >> What I'm wanting is a box (FreeBSD?) that can be placed between a >> fibre channel block device (like a RAID array), and a fibre channel >> host using that block device, and act as a block cache for that >> device, using the FreeBSD's memory. If it had a significant amount >> of memory, this could be very useful. > > > If you use the example scsi_target usermode > (usr/share/examples/scsi_target), then the buffer cache will be used > since its reads/writes are from usermode like normal. If you don't > want that behavior, you can set O_DIRECT in the open() call of the > backing store file. > > If you chose to modify the kernel side, you'd have to make sure your > accesses were through the VOP layer and then it would be cached. > > You should check to be sure the target mode performance meets your > expectations also. > I guess I would be using the user mode tool, unless there's another way? Your comment on performance also makes me a little worried about that now - do you think I would see a large performance hit? Thanks! Eric -- ------------------------------------------------------------------------ Eric Anderson Sr. Systems Administrator Centaur Technology Anything that works is better than anything that doesn't. ------------------------------------------------------------------------