David O'Brien wrote:
> On Sun, Apr 24, 2011 at 08:58:58AM +0000, Alexander Motin wrote:
>> Switch the GENERIC kernels for all architectures to the new CAM-based ATA
>> stack. It means that all legacy ATA drivers are disabled and replaced by
>> respective CAM drivers. If you are using ATA device names in /etc/fstab or
>> other places, make sure to update them respectively (adX -> adaY,
>> acdX -> cdY, afdX -> daY, astX -> saY, where 'Y's are the sequential
>> numbers for each type in order of detection, unless configured otherwise
>> with tunables, see cam(4)).
> I apologize if I missed a past discussion... but wasn't CAM designed
> so that all disk-like things would be 'da' (direct access) irregardless
> of underling protocol (SCSI/SAS/PATA/SATA)? "afdX -> daY" above helps
> suggest this. Wasn't that the reason we moved from 'sd' to 'da'?
> At least this was the impression on freebsd-current@ back when we when
> thru this in 1999 (e.g., <36EFF7C2.41C67EA6@whistle.com>,
> <firstname.lastname@example.org>, <email@example.com>,
CAM unifies the way to execute commands on devices with different
transports. That is why after this change afdX become daY and acdX
become cdY -- they all use SCSI command set. adaX same time stays on
it's own because it is ATA and uses different peripheral driver. It was
one of options to go by emulation way, translating SCSI commands into
ATA. That would turned all direct access devices into SCSI and daX, but
we went other way to not implement additional state machines for this
translation, since existing ata(4) state machine was horrible and we
prefer to drop it completely.
> Now ATA-CAM is the default, why aren't disks devices named by the
> established CAM names?
> If we're not going to call CAM controlled ATA disks "da", then why not
> keep the existing "ad" and "ar" given "ad" stood for "ATA-Disk" and
> "ATA-RAID" -- you're still calling the subsystem "ata".
What's about ad and ada, there is about 18 month history of early
adopting this new ATA stack. Using same name initially wasn't possible
due to collisions old stack, change now -- due to many adopted systems.
What's about ar, it is not so principal to me. With new names I was
trying to mimic other GEOMs behavior. But if people decide otherwise, I
see no problem to change it now.
> Otherwise, we can just recycle email from 1999 where folks didn't
> see much value in the sd->da change.
Sorry, I wasn't there in 1990s to speak about that change.