RE: iFCP as an IP Storage Work Item

["Y P Cheng" <ycheng@advansys.com>]

> As far as FCP stacks go, it is a truism that no OS
> (host) has a native FCP stack. Today.  (Stay tuned, though;
> Blackcomb AS is going to be rather interesting)
>
> That's why the HBA rules.  It's the entity performing
> all the translation between what the OSes see as a pure
> SCSI universe and the real (or virtual) device FC universe.
> Had we native motherboard FC physical interfaces and OS
> FCP stacks, we would not need FC HBAs.

With native motherboard FC chips, the BIOS has the necessary code to access
the chip. After booting, the OS transition from BIOS to the chip device
driver.  There is no FCP stack.  There is only the device driver code
supplied by the chip manufacturer. (In other words, different FC chips have
different drivers.)

> But, that's hosts.  Consider the world of devices for
> a moment.  No one can argue that there are not a
> plethora of FC devices today, all with FCP stacks by
> definition.  Plus, many FC devices today are not just
> one FC port but multiple, with multiple WWPN and one WWNN
> to achieve higher RAS characteristics.

You are confused between the device driver and TCP stack.  Most RAID
manufacturers use SDK, Software Development Kit, from HBA manufacturers.
The SDK allows RTOS to build device drivers for the ICs.  The ICs generate
FCP packets.  Unlike TCP/IP, the Fibre Channel IC device drivers are not
aware of the format of the FCP packets.  Therefore, they can not be called
the FCP stack.

> So while your statement
> > iFCP as way to keep your investment in FCP stacks is a very
> > weak argument.
> is certainly true for hosts (initiators), it is certainly
> not true for devices (targets).

No, Julo is correct.  The argument is very weak.  The statement is
especially weak if an iSCSI adapter uses the same implementation as an FCP
adapter.  In the adapter implementation, the iSCSI header will be added by
the adapter.  There won't be an iSCSI stack in the OS for adding the iSCSI
headers.  Of course, a stack implementation of iSCSI in an OS is likely
although not efficiently.  Most manufacturers with high performance in mind
will choose to put the iSCSI stack inside the adapter, not in the OS.

Y.P. Cheng, Connectcom Solutions.