Removing data group transfers

gop at us.ibm.com gop at us.ibm.com
Wed May 10 08:55:20 PDT 2000


* From the T10 Reflector (t10 at t10.org), posted by:
* gop at us.ibm.com
*
At the next t10 meeting I am going to request that data group transfers not
be allowed during f-160 data transfers. The effect of this would be that
Ultra 320 devices, when running at the 320 Megabytes/sec data rate, would
only support packetized. For any slower data rate using DT either data
group transfers or packetized transfers would still be allowed.
There are several reasons for doing this. Some of them are:
-Makes the f-160 implementations easier because data group transfers would
not have to be implemented at the high data rates.
-The performance of data group transfers at the f-160 data rates does not
give a significant performance boost over f-80 devices. This is especially
true now that training has been added in. I will have graphs that show this
at the next SPI-4 working group.
-Data group transfers require the handling of pad bytes at the lowest level
of the SCSI interconnect. This adds in complexity especially on the
initiator which must be monitoring the P_CRCA signal and be ready, on
request from the target, to the throw out a CRC at any point in the
transfer.
-With no data group transfers SPI-4 could take advantage of the fact that
all transfers are 4 bytes long. This means the confirming handshake line
could run at half the frequency with every transition confirming 4 bytes
received instead of the current 2.

Bye for now,
George Penokie

Dept Z9V  114-2 N212
E-Mail:    gop at us.ibm.com
Internal:  553-5208
External: 507-253-5208   FAX: 507-253-2880


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