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List:       apache-modperl
Subject:    Re: Repost: Anyone using "virtual server" for mod_perl hosts?
From:       Malcolm Beattie <mbeattie () sable ! ox ! ac ! uk>
Date:       2001-01-31 13:52:41
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Robert Landrum writes:
> The S390 appearently runs some type of software that allows you to 
> set limits on your partitions, so no matter what, you always have 
> some percentage of the CPU at your disposal.

It's called VM and it's a lot more flexible than that.

> This is not the case with the Sun 10000.  With that machine, you must 
> explicity set which processors you want partitioned to your virtual 
> box.  With a 16 processor Sun 10000, you could set up four, four 
> processor Sun virtual machines, all sharing the same hard drives and 
> external adapters (NIC cards and serial ports).

Exactly: with E10k (and IBM NUMAQ) you are limited to splitting
things up at a "quad" (4 processor) boundary.

> Large systems like this are dying,

I think you misspelled "beginning to be even more popular" :-)

>                                    as they generally require much 
> more knowledge than simply establishing a server farm of the same 
> capabilities.  It's much easier to higher people to set up 50 boxes 
> (linux, NT, BSD, Solaris) than it is to find people that can 
> configure an S390 or Sun 10000.

50 boxes: no problem. 200 boxes: 5 racks or 1U, getting messy.
1000 boxes: admin nightmare. Plus you don't get much too many
built-in reliability features with a 1U box. Now consider that you can
run *thousands* of separate Linux images on a S/390 box which consists
of just one or two frames (i.e. the size of one or two racks). It'll
need hooking up to a rack or few of disks too. Far less floor space,
far less power, far more reliable, far fewer cables and mess, very
easy to create a new virtual machine (minutes), pretty much all
maintenance and upgrading is concurrent and you can admin the whole
lot from one place. Now isn't that worth having to learn a bit about
how to admin a VM system? Especially since you wouldn't want some
random cheap admin looking after that many boxes and customers anyway.

There was a test/benchmark done where more and more Linux virtual
machines were added to a system, each running Apache or INN or being
a client image pulling data from the server images. The experiment
was to see how many images the system could sustain. At 30000 images
the server images were still providing subsecond response time. The
system finally started thrashing at 41400 concurrent virtual machines.
I can dig out refs if people want (it was David Boyes who did it, if
I recall). In practical terms, you can put thousands of virtual
machines on one system: there are big advantages to sharing one large
machine. The most recent big name to go Linux/390 is Telia, the
Swedish Telco. See http://www.silicon.com/a41413 for an article about
it (yeah, I get a quote :-).

--Malcolm

-- 
Malcolm Beattie <mbeattie@sable.ox.ac.uk>
Unix Systems Programmer
Oxford University Computing Services

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