HPE OneView

Re: VirtualConnect and bandwidth allocation in operation?

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VirtualConnect and bandwidth allocation in operation?

My question is regarding the dynamic bandwidth capabilites in VirtualConnect as defined by OneView setttings for "Preferred" and "Maximum" bandwidth. As I understand it there are three components that play some role in how much bandwidth is allocated to a particular network:

The first is in the given Network's configured Preferred bandwidth (default 2.5 Gb/s) and Maximum bandwidth (I'm seeing a default of 50 Gb/s in my OV Composer 5.40) - I'm unsure if this Network Maximum bandwidth this should be changed from default 50Gb/s to either the maximum supported by the installed VirtualConnect (40 GB for VC SE 40Gb F8 Module) or set to the maximum supported by the installed compute module CNA adapter (20 GB for Synergy3820c adapter) or just left at the default 50Gb/s despite none the equipment in my Synergy environment being able to handle 50GB - I only have 20GB Interconnects?

The second is in the Network Set's (to which the above-referenced network is assigned) Preferred bandwidth (default 2.5 Gb/s) setting and Maximum bandwidth setting of 50Gb/s - again I'm unsure if this Network Set Maximum bandwidth this should be changed to either the maximum supported by the installed VirtualConnect 40GB, the maximum supported by the installed compute module CNA adapter 20GB, or left at the default 50Gb/s?

The third is the configuration of the Connections in the Profile/Profile Template option for Requested bandwidth - which appears to pull in the Preferred Bandwidth value setting or either the Network or Network Set you selected for this connection.

I do understand that the *combined* Requested bandwidth allocations of all my Connections assigned to the interfaces on my CNA device (including the 8GB bandwidth reserved for FC) cannot exceed the total bandwidth of that device. So for my 20Gb 3820c adapters, the Requested Bandwidth of my three Connections, each configured for one of my three unique Network Sets cannot exceed 12Gb in aggregate, because the other 8Gb being reserved for FC connections. My real question is: exactly how DYNAMIC is the bandwidth allocation to these connections during normal operation and by what mechanism is it changed on the fly by the Virtualconnect? For example, Let's say I configure a Connection for management Network/Netork Set with Preferred Bandwidth of 1Gb, a Connection for vmotion Network and Network Set also with Preferred Bandwidth of 1Gb, and connection for a number of vm Networks in a single vm Network Set with Preferred Bandwidth of 10Gb. Assuming very little VM network traffic is occurring and I initiate a large-scale vmotion, I understand that since there is a large amount of bandwidth available beyond the 1Gb Preferred Bandwidth guarantee I have set for the connection carrying my vMotion Network/Network Set, that connection will burst or scale up beyond 1Gb/s to use any and all available overhead - which is what I want it to do. But what if during the vmotion operation a large amount of network traffic starts to occur within my vm Networks/Network set? How quickly is the need for reallocation of bandwidth detected, and how quickly does the reallocation occur? Does the VC detect this immediately and change the allocations on the fly to drop the vmotion Connection back to 1 GB and allow the vm Network Connection to grab back it's preferred bandwidth guarantee of 10GB, or does that evaluation only occur on a polling interval (every 30/60/120 secs, etc.) where samples are taken in order to calculate any needed bandwidth adjustments? It's important beacuse if it's based on periodic sampling, there would be some period of time that my vm network is in dire need of additional currently-consumed-by-vmotion bandwidth to get back up to it's guaranteed minimum 10Gb. So by what mechanism / interval / etc. are these Preferred Bandwidth guarantees evaluated and any needed reallocations enforced?

I have looked at the OneView Server profile connections settings Help as well as the Networks > Preferred and Maximum Bandwidth and don't see anything explaining how this occurs during normal operation. 


Re: VirtualConnect and bandwidth allocation in operation?

These terms can be viewed as a bit confusing.

  • Preferred - Only set within a Network or Network Set resource, which can be viewed as the "minimum" or "default" bandwidth to set for a connection.
  • Maximum - Only set within a Network or Network Set resource, which is the maximum bandwidth to be allowed for a connection.
  • Requested - Only set within a Connection of a Server Profile Template or Server Profile resoure, and defaults to the Preferred value set within the Network or Network Set.

c-Class Virtual Connect implemented a Minimum and Maximum feature, to where if a FlexNIC wasn't transmitting, then other FlexNICs could consume more bandwidth, up to the maximum allowed by the physical port (or Maximum value was set to).  HPE OneView doesn't allow one to set the Maximum within the Server Profile, but the Network/Network Set Maximum is configured when the FlexNIC is instantiated.  Keep in mind that you will not "see" the maxmimum "link speed" value in the OS.  You will  always see the maximum port speed allowed by the adapter.  Also, as you pointed out, you cannot oversubscribe the Connections.  Meaning, that the total requested bandwidth must not exceed that of the parent port.  So if the adpater supports maximum of 20Gb, then all of the requested bandwidth cannot equal more than 20Gb.  You would also have to take into account the FlexHBA, as that is always guaranteed the bandwidth, and will never "flutuate" or "dynamically change".

So how does this work?  Well, this is time slicing within the NIC ASIC.  It is very similar to "shares" within a hypervisor.  The "Requested" bandwidth is the minimum allocated, and a "share" is calculated from the maximum bandwidth of the parent port.  So if all connections are set to 2.5, then all connnections/FlexNICs will get equal time slice to the NIC ASIC.

What do you set the maximum bandwidth to?  You can leave it at 50Gb, even though your adapters only support 20Gb, and are connected to 20Gb capable fabric modules.  OneView defaults to that value because of the fabric modules it supports.

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