[MacPerl] Re: hot-swappable hardware

[Jonathan Eunice <develop@illuminata.com>]

Patrick Beart wrote:

>	Sun's OS is so robust that you can change RAM and (I'm told) the
>entire motherboard while the machine is running!  I'm not talking about
>peripherals, here. I mean the internal components. 

Andrew M. Langmead (aml@world.std.com) wrote:

>It seems that Apple started some work in that direction, but the
>project never came to completion. Their Tech Note 31 discussed some of
>the API they were developing to inform the programmer that fundamental
>hardware had changed. 


Robustness and Sun's Solaris are occasional fellow travelers, but they're 
hardly inseparable!  Note also that while hot-swapping components >is<
impressive, it's more a matter of being able to "vary off" the component 
from an OS and hardware point of view, having enough power management
electronics around to avoid disastrous arcing when a powered component
is removed and its replacement added, and then being able to "vary on"
the new component.  It's hard, but not awesomely so.  Many storage vendors
have done this for SCSI busses, and some Hot Plug PCI implementations 
are now appearing.  Hot swap can really help cut downtime, but it's more 
connected to OS functionality than to robustness. 

It's also not very interesting in the workstations and small servers that 
are
the core of Apple's business.  Most of these smaller systems only have 
one CPU and maybe a few DIMMs of RAM.  Vary one of them off and you
might as well have the whole system down for all the work they'll get done
in the meantime.  Those purchasing desktops and basic servers are also
prone to make decisions based on price and price/performance well before
considering online maintainability.  Adding hot swappability is still a 
fairly 
expensive engineering exercise, it being not yet an off-the-shelf thing
for system components.  It does make some sense for FireWire, USB, and 
Fibre Channel connections.  For Sun, it makes perfect sense, esp. for
those lucky few who can buy a 64-processor E10000 super-server with 
gigabytes of RAM and thousands of disk spindles.  One heck of a Perl
engine!  

...we now return to our regularly scheduled MacPerl programming
   already in progress...



Jonathan Eunice

(who in spare moments when he's not programming 
Perl, is a technology analyst covering server technologies)

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