dal at endl.com
Fri Nov 4 16:51:46 PST 1994
Minutes of the November 2 Low Cost Fabric Ad Hoc
The Low Cost Fabric Ad Hoc authorized by X3T11 which met at the Denver
Stapleton Red Lion on November 2 was attended by the following:
Dal Allan ENDL Jean Kodama QLogic
Charles Binford AT&T GIS/NCR John Lohmeyer AT&T GIS/NCR
Kurt Chan Hewlett Packard Kumar Malavalli Hewlett Packard CNO
Jim Coomes Seagate Bob Mayer Hewlett Packard
Richard Dugan Hewlett Packard Jim McGrath Quantum
Dave Ford Cambex Robin Purohit Hewlett Packard CNO
Giles Frazier IBM Bob Snively Sun Microsystems
Gene Freeman AT&T GIS/NCR Ken Thompson AT&T GIS/NCR
Stillman Gates Adaptec Horst Truestedt IBM
Norm Harris Adaptec Fanny Wong IBM
The minutes of the ad hoc are being distributed on the SCSI and Fibre
Channel reflectors, as the attendees were a mix of both groups.
The objective of the ad hoc was to table all the ideas which are presently
circulating on how to configure Fibre Channel for the best performance at
the lowest cost. Once a base which included all the ideas was established,
individuals would be volunteered to pursue those in which they had an
interest, and report on their merits.
Heterogeneous Operation: Jim McGrath was the only attendee present who had
come prepared with a presentation. A joint press release of Quantum, Seagate
and Hewlett Packard was included in the handout, in which the three
committed to Fast20 and Fibre Channel Arbitrated Loop for SCSI disk drives.
The primary point Jim made was that to become a mainstream interface, Fibre
Channel had to be able to connect devices of heterogeneous speeds. Although
this capability exists with switches, it is not cheap enough.
He emphasized that Fibre Channel had to be popularly priced, and not be seen
as the preserve of supercomputing and high end workstations. At present, the
FC-AL has no provision to share devices of various speeds, and is perceived
as a 100 MBs solution only, and not at low cost 25 MBs.
As the least expensice fabric alternative, Jim wanted FC-AL to provide the
equivalent functionality to mixing SCSI-2 and FAST-20 devices on the same
bus. He proposed alternatives such as small loops combined by a low cost
switch, and a way to expand the FC-AL protocol to alternate between 25 MBs
operation on the loop and faster speeds between faster ports.
Multiplexed Low Speed Ports: Dal Allan presented hardware considerations
and the application possiblities for an alternative to the loop which used
radial connects to low speed devices and relied on buffers to speed match
and multiplex transfers over to high speed ports connected on the host side.
F_Ports: Robin Purohit described the considerations involved in the design
of an F_Port which was attempting to provide maximum performance between two
loops on opposite sides of a switched fabric. The problems of buffering on
the receive side and flow control were expensive in management and
Horst Truestedt described the opposite extreme in which loop devices could
transfer only one frame every arbitration cycle through the F_Port to the
fabric. This would simulate the behavior of a single N_Port being serviced
by an F_Port plus the overhead of arbitration between frames. This reduced
the complexity of the F_Port design but at an unknown performance loss.
10-bit Interface: The possibility of using 10-bit interface between devices
physically close to each other was described by Kurt Chan and Dal Allan.
Kurt felt it might be possible to use the 10-bit interface currently being
designed but Dal thought the bus considerations required a layer which
accepted the 10-bit interface and adapted it to bus operation.
The immediate objective would be to achieve Gbaud operation at 1/4 speed
costs by eliminating the expense of serial transceivers. As the cost of
serial components fell and Gbaud became integrated, the parallel interface
would advance to higher transfer rates.
Summary: All of the above were actively debated by all attendees, and there
were contrary opinions expressed on every proposal. It was a very active and
highly participative morning. It cannot be said that any conclusions were
drawn or agreed to but we had a lot of fun....
Cost Elements: After lunch, cost bogies were established for mid-1996
availability of 25 MBs copper interface elements assuming Q100,000 ordering
by disk drive vendors of their parts and other units scaled accordingly.
+---------+ +---------+ +---------+ +---+-----+
| Host | | | |Packaging| |FCP|Disk |
| Adapter | | F_Port | | F_Port | | |Drive|
+---------+ +---------+ +---------+ +---+-----+
$70 - $150 $150 ? $10 ?
Jim insisted that an FC-AL front end operating at 25 MBs had to be priced
the same as single ended SCSI, and that was only $10 of the drive cost. Jim
was assuming in-house cost of an FC_AL front end (to avoid paying merchant
vendors the margin they needed to justify building a component).
There was a wide divergence of opinions on how cheaply an adapter could be
built with Bob Snively at $70 and Norm Harris at $150.
Kumar Malavalli and Robin Purohit felt that to be widely adopted, an F_Port
had to be built at a cost point of around $150.
The price of these elements to OEMs were expected to be 3-4 times as high,
depending on the amount of R&D recovery.
No quantitative analysis is involved in these numbers. The purpose of the
exercise was to instill consciousness, awareness and quantify 'low-cost'.
These numbers were chosen by arguing amongst each other until the hubbub
subsided to an acceptable level.
Mixed Speed Solution: Jim McGrath ended the day by leading a design effort
to modify FC-AL to intermix devices of multiple speeds. His ideas ran into
strong opposition as severely impacting the present protocol and assumed
The alternative with minimum time to market and minimum impact on standards
was to operate a dual ported initiator running one loop at low speed and the
other at high speed. If redundancy was needed, use dual ported devices and
connect them to another dual-ported initiator.
Robin Purohit - assess cost impact and performance achievable by a single
frame transfer every arbitration cycle through an F_Port to a host.
Robin Purohit - assess cost and performance achievable by an F_Port designed
to provide up to 80% of loop bandwidth on one side of the fabric to a host
on the other.
Horst Truested/Jim Coomes - assess performance impact of switching speeds
based on initiator control of the loop speed, using the LR circuit as a way
to bypass low speed devices during high speed transfers, and vice-versa.
Kurt Chan - estimate cost considerations of packaging and components for a
10-bit bus version of FC-AL.
Norm Harris/Stillman Gates - estimate considerations/costs involved in a
multiplexing adapter which has radial connects to devices.
Next Meeting: None scheduled.
The above action items and further LCF discussions will be part of the
Fibre Channel working group, scheduled for Thurday of X3T11 plenary week.
If other ad hocs are presumed necessary to pursue specific ideas/projects,
they will be scheduled by someone who wants to lead such an activity.
The time for completion of the above action items and report on them is
December 8 at the San Jose Red Lion.
My thanks to all who attended. Please advise of any errors or omissions so
they can be corrected before these minutes are submitted in my reports to
X3T10 and X3T11.
I. Dal Allan
More information about the T10