[illumos-Developer] Changing sd_io_time to 8?

[Joerg Schilling]

"Garrett D'Amore" <garrett at damore.org> wrote:

> > Well, you need SCSI commands for CD-ROMs even when they are connected via ATA.
> > 
> > I am not sure that this would really help.
>
> Yes, but the SCSI commands and the support logic you need for cdroms are
> quite different from what you need for disks, even though there is a
> large area of overlap.  There's a reason that these are specified by
> different parts of the SCSI standards. :-)

Some of the SCSI commands supported by CD-ROMs are from the general list, some 
are from the disk services and some are multi-media commands.

Harddisks support general and disk services commands but of course no 
multi-media commands.

These different command sets exist just to make things easier to administer in 
the standard commitee.

The split happened aprox. 20 years ago, when the SCSI transport standard has 
been removed from the SCSI protocol to allow different transports to be used by 
the same devices without a need to repeat everything.

The Sun SCSA architecture has been written in a way that fits to this layering.

There is a driver that creates high level requests.

There is a glue layer in the middle

and there is a adapter layer that knows about the was to actually send commands 
though specific hardware.



Linux did separate PATA and SCSI (SATA was integrated) and Linux has more 
problems than Solaris.......


Jörg

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