[Info-vax] booting vaxstation off alpha

[Chris Scheers]

Johnny Billquist wrote:
> On 2013-02-11 13:44, Stephen Hoffman wrote:
>> On 2013-02-11 07:54:11 +0000, Hans Vlems said:
>>
>>> DECnet over DSSI works fine, provided you get the incantations right.
>>> All I tried was CTERM and FAL and both worked as expected (reliable
>>> albeit slow).
>>> Another example of an undocumented, unsupported feature that works
>>> alright.
>>
>> Not that there is even a remote chance of seeing DSSI gear around, nor
>> any likelihood of IP over FC nor connections, but...
>>
>> If you ran any tests[1] with that, how well does that "albeit slow"
>> connection perform as compared with slow Ethernet?  CI wasn't known for
>> its network performance, as compared with DECnet over even then-current
>> 10 Mb Ethernet, and usual recommendations back then had CI at higher
>> cost as a backup connection.  I can't see DSSI being much better in that
>> regard.
> 
> That sounds weird. Do you know why?
> I mean, CI was after all two redundant full duplex 70 Mbit/s channels, 
> compared to the half-duplex 10Mbit/s ethernet. Not to mention the fact 
> that the MTU of CI is much larger.

IIRC, CI is a form of token ring.  In particular, it has various "slots" 
that circulate that are allocated to applications.

Again, from memory, DECnet, if configured, got about 10% of the 
bandwidth. So DECnet had a theoretical bandwidth of 7MB/sec on the CI 
vs. 10MB/sec on the Ethernet.

Also, you needed to have Ethernet available to boot your cluster. 
DECnet on CI was configured after you had booted.

We used to have a 780/785 cluster where we configured the DECnet channel 
on CI.  It had lower priority than the Ethernet.  It did save us a few 
times when "stuff happened" on the Ethernet that disrupted 
communications.  We would loose our terminal servers, but the DECnet/CI 
was enough to keep the cluster from crashing.  When the Ethernet came 
back, everything could continue.

-- 
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Chris Scheers, Applied Synergy, Inc.

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