FC Tape Profile Position

Stewart Wyatt stewart at hpbs3928.boi.hp.com
Fri Nov 14 07:16:24 PST 1997


* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
* Stewart Wyatt <stewart at hpbs3928.boi.hp.com>
*


Tape Profile Position of HP CPB

Stewart Wyatt, Controller Hardware, Hewlett Packard CPB, 
Boise, Idaho.
(CPB is Hewlett Packard's tape drive division.)

November 13, 1997

At the tape profile meeting in Palm Springs, Dal Allan 
suggested that the participants post their positions and 
assumptions relative to the selection of class 2 or 3.  I think that 
one of the problems that the working group has is that we have 
not had a consistent set of assumptions and expectations.  I have 
been in favor of providing a profile for both classes of service 
though I intend to implement class 3 first.  I would like to 
support that decision by answering some of the assumptions that 
I have heard promoted in the profile discussions and presenting 
some of my own assumptions.

1. Fibre Channel has to reach cost parity with SCSI for it to 
become a widely accepted interface. 

 I hear this assumption everywhere Fibre Channel is discussed 
except in the tape profile meetings.  When Seagate introduced 
the first Fibre Channel drives, they advertised that they were at 
cost parity with Differential SCSI and would be at cost parity 
with Single Ended SCSI by the second year.  Our marketing 
data is that most customers will not switch from SCSI to Fibre 
Channel without the products being at cost parity and a 
compelling performance advantage.  It will, of course, require a 
large volume of products to drive the price down.  This creates a 
"catch 22" situation.  Adding expensive features to all products 
not required by the large volume applications will increase the 
price of the products and slow adoption of the standard.

2. Creating a class 2 profile for tapes will influence disks to adopt 
class 2.  

This argument is without any historical precedence.   Last year 
(1996) 106.7 million disks shipped generating  $25.2 billion in 
factory revenue while 5.2 million tapes shipped generating $3.0 
billion in factory revenue.  The tape industry is so small that it 
has little influence with component vendors.  The fact that we 
are starting a tape profile several years after the disk profile 
started demonstrates how tapes follow disks.  With its smaller 
volumes and revenues, the tape industry has relied heavily on 
leveraging disk industry developments to make new product 
development cost effective.  Most tape companies are not 
vertically integrated and are not able to develop the hardware 
(asics) for interface solutions.  A typical tape product today is 
using SCSI hardware developed originally for a disk drive 
application.  

There are interface solutions available that support multiple 
classes of service that are designed for host bus adapter 
solutions.   Typically these parts have a PCI interface on the 
backend to enable direct access to host memory.  These products 
cost too much, are too large and consume too much power for 
consideration in a peripheral product.  Typically tape 
applications buy a "stand alone" interface chip or integrate an 
"interface core" with other functionality into a tape controller 
ASIC.  All of the available designs, without exception, are 
strictly designed around the PLDA requirements.  None of the 
suppliers have any plans to support class 2 operation in 
hardware. The relatively small volumes of the tape industry 
make it very difficult to interest an ASIC supplier to develop 
hardware that has unique characteristics for tapes.

3. Class 3 offers the fastest path to market.

As stated in the previous paragraph, class 3 designs are available 
and proven while class 2 hardware has to be developed giving 
class 3 an enormous time to market advantage.  Class 3 
solutions exist which have been proven in disk applications 
dramatically decreasing risk and development costs.

4. Class 2 offers better support for queuing and fabric support.

This position is widely held by people who ought to know.  The 
issues are out of my range of experience. I assume that the class 
2 promoters know what they are talking about.  The question 
that comes to mind is how soon these types of applications are 
needed.  I don't think that these requirements will occur in the 
next few years.  I think the current applications are more like 
locally backing up a RAID box on a server.

5. Tape manufacturers all support class 2.

While some manufacturers support class 2, HP, among others 
supports class 3.  In the Palm Springs meetings several manufacturers 
voiced support for a class 3 profile.

6. Adopting class 3 precludes class 2, or its corollary, we only 
want to support one class of service.

The first statement is only true if class 3 meets all of the market 
needs and no large customer or group of customers requires 
class 2 service as a purchase requirement for their application. 
The corollary is purely wishful thinking.  Those who stay in 
business will support whatever features their customers require.  
Customer requirements will change over time.  We supported 
asynchronous SCSI until Fast SCSI came along.  After 
developing fast we implemented wide.  Every generation of 
products incorporates new controller features as soon as there is 
enough market demand to make them cost effective.  In a few 
years products may support both classes of service to allow 
systems integrators a choice - we offer SCSI products that 
support a large number of interface options today, why will 
Fibre Channel be different?

Conclusion:

I have been involved in the tape profile discussions since they 
began.  The arguments for selection of class of service have all 
been based on technical issues.  I hope that this memo brings 
some implementation and market perspectives to the 
discussions. 

The proponents of the class 2 and class 3 approach are deeply 
entrenched in their respective positions. Additional discussions 
are unlikely to cause anyone to change their mind.  There are 
significant merits to both approaches which has brought the 
effort to choose one class of service exclusively to a complete 
deadlock.  Class 3 solutions are already shipping and will 
continue to be shipped regardless of any decision made by the 
standards community.   

Realistically the only decision left to the standards community is 
whether profiles supporting both classes of service will be 
developed by the standards group or will be developed 
privately. I strongly favor developing profiles supporting both 
classes of service in the working group.  Adequate time has 
already been spent discussing the relative merits of the two 
proposals.  Delaying product implementation for continued 
debate will only harm the industry and delay or imperil to 
acceptance of Fibre Channel.

--

Stewart Wyatt                                 stewart_wyatt at hp.com
CPB Boise Controller Group                    Phone: (208) 396-3594
Hewlett Packard CPB Boise, PO Box 15, MS 477, Boise, ID 83707
*
* For T10 Reflector information, send a message with
* 'info t10' (no quotes) in the message body to majordomo at symbios.com




More information about the T10 mailing list