But according to the datasheets, upgrading, say, an H06 to an H13
"requires planned down time", so if you started small and then want to
grow, the only feasible (non-down-time) upgrade path is to buy a 2nd
mainframe, which, as you point out "won't scale painlessly".
With a COTS based system, you work with a cluster configuration from the
start (without requiring additional licenses), and have a rather more
granular and disruption-free upgrade path.
And because it is designed from the ground up as a cluster, it is
designed to be maintainable WHILE WORKING. Replacing any hardware
component of the cluster (ECC memory, CPU, I/O board, main board,
network component, rack, ...) can be done while the system is running.
So there isn't really any *functional* advantage to using a mainframe.
The question is whether you want to be running a cluster of, say, 2 - 5
mainframes, or, say, 10 - 500 COTS boxen. I.e. "what do you want to
spend your money on".
And no, you should not then have a bunch of sysadmins running around
manually managing those 500 COTS boxen. That's supposed to be automated...
WFK
On 05/25/17 16:22, John Campbell wrote:
> As I recall from Appendix A of the "Linux for S/390" redbook, the S/390
> (and, likely, zSeries) is designed to be maintainable WHILE WORKING.
>
> The multi-dimensional ECC memory allows a memory card to be replaced WHILE
> the system is running. Likewise, power supplies the CPs.
>
> I have to agree that the "second" zSeries box won't scale painlessly; The
> work to load balance would NOT be fun (and the second box has its own
> issues w/r/t the management team, too).
>
> I recall, when dealing with the idea of putting an S/390 into a Universal
> Server Farm in Secaucus, NJ (I had some fun helping define the various
> networks as this predated the "hyperchannel" within the BFI ("Big Iron") as
> part of this USF integration) when it was killed for non-technical reasons.
>
> -soup
>
> On Thu, May 25, 2017 at 8:41 AM, Philipp Kern <pk...@debian.org> wrote:
>
>> On 24.05.2017 00:03, John Campbell wrote:
>>> Cool...
>>>
>>> Though the real key is that the mainframe is designed for something at or
>>> beyond five 9s (99.999%) uptime.
>>>
>>> [HUMOR]
>>> Heard from a Tandem guy: "Your application, as critical as it is, is on
>> a
>>> nine 5s (55.5555555%) platform."
>>> [/HUMOR]
>>
>> Mostly you trade complexity in hardware with complexity in software.
>> Mainframes do not scale limitless either, so you trade being able to
>> grow your service by adding hardware with doing it within the boundaries
>> of a sysplex.
>>
>> Your first statement is also imprecise. It's designed for five 9s
>> excluding scheduled downtime. If you use the fact that hardware is
>> unrealiable (after subtracting your grossly overstated unreliability) to
>> your advantage, you end up with a system where any component can fail
>> and it doesn't matter. You win.
>>
>> Again, it then comes down to the trade-off question if you're willing to
>> pay for the smart software and the smart brains to maintain it rather
>> than paying IBM to provide service for the mainframe.
>>
>> Kind regards
>> Philipp Kern
>>
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>>
>
>
>
> --
> John R. Campbell Speaker to Machines souperb at gmail dot
> com
> MacOS X proved it was easier to make Unix user-friendly than to fix Windows
> "It doesn't matter how well-crafted a system is to eliminate errors;
> Regardless
> of any and all checks and balances in place, all systems will fail because,
> somewhere, there is meat in the loop." - me
>
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>
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