[CentOS] Sharing RAM between VM

Larry larry at itsbg.net
Thu Apr 16 10:16:16 UTC 2009

> Depends what your goal is, if you want to run a cluster with shared
> memory between systems, you typically need a very high speed interconnect
> and very low latencies, your not likely to achieve this within VMs.
> Your original message just talked about sharing ram between VMs, you
> didn't mention why you were specifically interested in doing that.
> > nate, which vmware you use? VMware ESXi or VMWare Server or something
> > else?
> Whenever possible I'd use ESXi, I happen to use vmware server on
> the system that is sending my email because it's old and ESXi doesn't
> support the 3ware 8006-2 SATA card in it. Check the hardware
> compatibility list, the list is fairly short for some things like SATA,
> though ESX 4 is due out in the coming week(s) which is supposed to
> dramatically improve SATA support.
> Note that out of the box ESXi(with the free license) doesn't support
> snapshots or cold migrations(between servers) at least last time
> I checked the feature comparisons sheet. I'll be installing about
> 12 new ESXi systems soon. VMware server does not support page
> sharing or memory ballooning, and does support snapshots. I use
> vmware server 1.x, probably will go to 2.x in the next couple months.

nate, thanks a lot for this answer. I'll give ESXi a try. (Maybe I'll
wait till next version)

> > p.s. Stable xen, has ballooning. You can say for every VM:
> > memory=1024MB, max-mem=2048MB. And you can tweak the memory "manually",
> > without having to restart the VM and without any other problems.
> That's not memory ballooning, at least not in the vmware world, and
> you can do the same in vmware, though if you decide to drop the
> amount of physical memory allocated to the guest without having the
> guest free up that memory you'll go into swap pretty quick, so it's
> not a practice I do, really ever.
> If Xen has a specific balloon driver like vmware and inflates the
> balloon when you change the memory settings that would be pretty
> cool, as far as I know vmware does not do that, the balloon only
> kicks in when host memory is low, not when you decide you want to
> resize the guest.

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