I was pained around two months back
when one of our marketing people made a snide comment
about running MVS on VM "if you want your performance to drop".
(My words, not hers.) I had to bite my tounge, focus on
what we were discussing, and not go into a tirade about SIE.
Consider the term "insertion loss".
If you have cable television, or if you are a radio hobbyist,
you may have heard it before. The "insertion loss" for z/VM
is very small, thanks to SIE assist. The "insertion loss"
for VMware is much higher, more like it used to be for VM/370,
or perhaps worse because the PC-class systems lack that uniform I/O.
And VMware is, like Mark said, less "mature" than z/VM.
But it REALLY IS A HYPERVISOR.
On Mon, 11 Oct 2004, Tom Duerbusch wrote:
> VMWare is NOT VM..it is more like LPAR.
> You need XX MBs of ram for VMWare.
> If you are running something that needed 512MBs to run and you want to
> run 4 copies, then your real storage needed would be (512MB *4 + XX
> MBs). VMWare can do some paging at a significant impact to performance,
> so don't let it.
At least they told you that VMware virtual machines *can* be paged.
Originally, VMware always let the host OS deal with virtual machine
memory. Later, VMware would try to pin-down some host storage
specifically for virtual machine use, a little like V=R. I run
VMware on my newest box at home and only this past weekend flipped
the switch to let guests page. (To me, that's the normal way
to run a virtual machine!)
VMware does have certain limits.
Again, I applaud what VMware (the company, and its architects)
have done, especially given what little was done for them by INTeL.
I can see, Tom, how you got your impression. But be aware that
the reality is that VMware is NOT LPAR. There ARE LPAR-like schemes
for PC-class hardware. VMware ain't one of them.
> VMWare seemed to be more akin to V=R with perferred guests. Dedicated
> scsi adapters, dedicated LAN cards, dedicated ....
Someone mis-presented VMware.
Many would expect the majority of VMware virtual machines
to have virtual disks much like z/VM minidisks. Just like on z/VM,
the disk(s) a guest owns can be virtual or attached. Networking too
is a lot more like z/VM:
"host only" == guest LAN
"bridged ethernet" == VSWITCH
But your impression is DEAD ON
in so far as z/VM and zSeries do a handier job
of creating virtual machines. I go back to the "up to a dozen"
virtual machines with VMware -vs- "dozens, hundreds, even thousands"
of virtual machines with z/VM. Practically, yeah, this is LPAR.
-- R;
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