Date: Fri, 20 Apr 2007 20:47:34 +0200 From: Bernard Buri <berni@ask-us.at> Cc: scsi@freebsd.org Subject: Re: Upcoming plans for CAM Message-ID: <46290AC6.9020608@ask-us.at> In-Reply-To: <4628E0DE.2090103@samsco.org> References: <4628E0DE.2090103@samsco.org>
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Scott Long wrote: > All, > > Now that the MPSAFE work is mostly done and settled, it's time to move > onto the next phase of the overall work. > this is great news! I've been working with the CAM layer in my last project, and I loved it. It is the most advanced scsi stack I've seen, so I'm glad it gets some refinement now. > ... > SATA and IDE transports, ATA protocol > ------------------------------------- > > The transport modularization work described above will allow non-SCSI > transports to be easily added. So, the next step is the long-promised > unification with IDE and SATA. Instead of hacks like atapicam and > atacam that try to force IDE/SATA into the SCSI model, a whole new > subtransport will be written that understands the topology and nature of > the devices, as well as natively understanding the ATA command set. > > There are still some interesting design questions that need to be > answered here. SATA controllers essentially use a star topology instead > of a bus topology. So does it make sense to treat all devices as each > having a private bus, or is it better to have a single virtual bus? > Also, ATAPI devices basically speak the SCSI protocol so they'll attach > to things like the 'cd' driver, but ATA disks speak ATA, which is very > different from SCSI. Should they get their own unique peripheral > device, or should they be part of the 'da' device? If they get their > own peripheral device, should they still generate '/dev/da' device > nodes, or should they retain the current '/dev/ad' naming? > I think that for the user, the device name doesn't really make a difference. Like with network interface cards, it is not a problem that some of them show up as fxp*, while others show up as myk*. As long as there is not a separate fxpconfig and mykconfig tool. I think for the way cam is desigend right now, it is more intuitive to have separate device names. In fact, I don't know much about ATA disks. I recognized recently, that SATA disks show up as /dev/sdX on linux while PATA disks show up as /dev/hdX. And SATA disks are said to be compatible to serial attached scsi. Does it mean that only PATA disks will be /dev/ad* ?
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