OSD CREATE

[Elliott, Robert (Hou)]

* From the T10 Reflector (t10 at t10.org), posted by:
* "Elliott, Robert (Hou)" <Robert.Elliott at compaq.com>
*

> -----Original Message-----
> From: hafner at almaden.ibm.com [mailto:hafner at almaden.ibm.com]

> Anybody want to bite off changing SAM to allow for 
> bi-directional data?
> 

A command dependent on this behavior would not work over any existing
transport protocols (SPI-3, FCP-2, etc).  An alternative mechanism would be
needed, although new transports could provide support for it to increase
performance.

Parallel SCSI - the target controls the I/O line and could change the bus
phase from DATA IN to DATA OUT as needed.

Fibre Channel - both READ DATA and WRITE DATA could be set to 1 in the
FCP_CMND IU (currently disallowed).  An extra FCP_DL field in the FCP_CMND
IU would be needed to indicate the data length for the extra data direction.
Sequence initiative transfer and credit management would become more
complicated.  Fibre Channel's full duplex nature would make this interesting
- both the read and write data could be transferred at the same time.

---
PC: Robert.Elliott at compaq.com
UNIX: relliott at hobbit.eng.hou.compaq.com

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