Jefe_Ryback
Contributor
Contributor

RAM reservation enforced when Directpath i/O device present

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Hello

Due some tests we needed to perform for a software having problems, we just configured a Intel network card as Directpath I/O against a Win2012R2 server. It's a 6.7 VMWare over HP Gen10 server.

The Directpath I/O procedure went smoth as all the documentation I found explained but when I tried to power on the VM an error appeared stating that I've to make a RAM reservation as big as the assigned vRAM tot hat machine (8GB in that case). When I did so, the VM turned on without any problem and everything works fine.

So, it's not that I'm having any problem (apart of the known limitations of having a pass-through devices); but I don't understand why it forced me for that RAM reservation and why I'm not able to find any mention to that requirement in any doc I'm reading regarding Directpath I/O. Have I done something wrong on the configuration? Did i miss some step?

Regards

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scott28tt
VMware Employee
VMware Employee

It is mentioned in the documentation, such as here for vSphere 7.0: https://docs.vmware.com/en/VMware-vSphere/7.0/com.vmware.vsphere.networking.doc/GUID-E34DB338-9770-4...


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Although I am a VMware employee I contribute to VMware Communities voluntarily (ie. not in any official capacity)
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scott28tt
VMware Employee
VMware Employee

It is mentioned in the documentation, such as here for vSphere 7.0: https://docs.vmware.com/en/VMware-vSphere/7.0/com.vmware.vsphere.networking.doc/GUID-E34DB338-9770-4...


-------------------------------------------------------------------------------------------------------------------------------------------------------------

Although I am a VMware employee I contribute to VMware Communities voluntarily (ie. not in any official capacity)
VMware Training & Certification blog
Jefe_Ryback
Contributor
Contributor

Hello scott28tt

Thanks for the link, all clear now. I was searching only on the documentation regarding directpath i/o (requisites, limitations and so on) and didn't thought on searching docs about the PCI device configuration itself (that I remembered as straightforward). My fault here, ^_^U

BTW, so far the test itself went OK but anyways I'm thinking on an alternative solution because all the directpath i/o limitations are a heavy burden. The loss on that machine availability options and the need of specific backup solutions are a pain. It's almost like having a bare metal server. And looking SR-IOV documentation, I see the limitations are more or less the same (I suppose the benefits there is just to be able to share between several VM a single PCI-E device, instead of the 1-to-1 assign on directpath I/O).

I'm not ranting on anyone, I suppose there's major engineering limitations on all that stuff that people way more knowledgeable than me have to deal with. It's just that realizing all those cons of the passthrough topic leave me a bad taste in the mouth like it's some lost opportunity somewhere to make those things could work way more fancy and flexible. As they are now, they just stole most of the major pros of having a VM the way I see it.

Regards and thanks again for the help

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