RFC: ATA to CAM integration patch
Alexander Motin
mav at FreeBSD.org
Sat Jun 27 16:31:22 UTC 2009
Ulrich Spörlein wrote:
> On Fri, 26.06.2009 at 21:47:26 +0300, Alexander Motin wrote:
>> [Great stuff]
>> - make sure that you will be able to boot if your SATA disk devices
>> name change from some ad4 to ada0;
>
> I, personally, think this is not very good idea. People are used to
> CAM-devices getting enumerated as da0, da1, etc. All the documentation
> talks about ad0 for ATA and da0 (plus camcontrol) for SCSI, USB,
> Firewire devices.
We should understand difference between transport and command set. SPI,
SAS, USB and FireWire are all just a transports for SCSI commands, and
their disk devices use the same SCSI-command disk driver "da". ATA disks
in this implementation are still use their native ATA commands, without
translating to SCSI. So "ada" is a completely separate driver, operating
disk devices supporting ATA, but _not_ a SCSI, command set.
Whatever name we would use for it, "ada" still will be separate driver.
It is not my whim. IMHO having two drivers with the same name is just a
time bomb, which will create problems in future. If somebody sure that
it won't, I will be glad to hear his technical opinion about how to
manage that properly, for example, in newbus.
> We also have fd0 and cd0 and should stick to
> two-letter-plus-number codes.
We also have a lot of longer disk driver names: aacd, amrd, mmcsd, ...
> So either make them all ad0 or da0. I'd
> vote for the latter, as that is what Linux is doing (more or less) and
> people are already familiar with USB drives or new SATA drives showing
> up as "SCSI drives, so they get the SCSI names".
The main difference is that in our case SATA is not SCSI! We are not
doing any emulation. CAM != SCSI any more! CAM = SCSI + ATA + whatever!
--
Alexander Motin
More information about the freebsd-current
mailing list