Date: Tue, 08 Feb 2005 15:10:04 -0700 From: Scott Long <scottl@freebsd.org> To: Dan Nelson <dnelson@allantgroup.com> Cc: freebsd-scsi@freebsd.org Subject: Re: how CAM/HBA probe for devices? Message-ID: <420938BC.6050800@freebsd.org> In-Reply-To: <20050208214956.GA3104@dan.emsphone.com> References: <E1CyYUO-0003tg-IT@cs1.cs.huji.ac.il> <4208F618.3000400@freebsd.org> <20050208214956.GA3104@dan.emsphone.com>
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Dan Nelson wrote: > In the last episode (Feb 08), Scott Long said: > >>For iSCSI, this obviously won't work. CAM has no concept of iSCSI >>addresses, and even if it did, doing a linear scan of even a small >>subnet would be prohibitively expensive. What is really needed is a >>new XPT layer that understands iSCSI. By this, I mean a layer that >>understands how to properly scan and detect targets, how to log into >>them, etc. It should also have a certain amount of flexibility so >>that hardware-assisted solutions can plug in and pick-and-choose the >>pieces they need from the transport layer. >> >>Lucent did an iSCSI initiator for FreeBSD 4.x a while back and I >>think they got around all of this by telling CAM not to auto-scan at >>boot, followed by having the driver announce devices to CAM directly >>(look at the ATAPI-CAM code for an example of how to do this) and do >>all the detection and login work behind CAM's back. This really >>should only be considered a hack though. If you're interested, I >>might be able to dig up the link to it. We never pursued integrating >>it to the FreeBSD tree because of very restrictive licensing terms on >>it. > > > The fibre-channel drivers (isp,mpt) must have been the first to have > hit this problem; do they do the same thing as atapicam? > Well, FC support in CAM is really limited to only simple arbitrated loops. Unless the driver and/or firmware gets involved and massages CAM's view of things, trying to do active-active loops and fabrics just isn't possible. Scott
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