Virtual Distributed Switches are a great feature of vSphere Enterprise Plus. If you have the oportunity to utlize them, I suggest not squandering it. vDS has many advantages that come with it, aside from the ease of configuring multiple hosts and time savings that comes with that. vDS switches also offer enhanced vMotion network support, Private VLANs, and inbound and outbound traffic shaping.
As I’m sure many of you know, vDS switches require vCenter… seems kind of obvious for a distributed component, but this brings up a valid concern in peoples minds:
What happens to my vDS network if vCenter where to fail completely. Will this bring down my network for the hosts?
The short answer is, no. Don’t worry, vCenter is not a single point of failure for these types of networking configurations. If you lose vCenter, you’ve just lost centralized management capability though vSphere Client (which for vDS switches is all management capability), but the virtual networking stays intact and fully functioning… similar to how VMs stay functional on hosts after a vCenter failure. Virtual Distributed Switches are made up of two distinct elements, the control plane and the data plane. With Virtual Standard Switches (vSS) these two components are bundled together and can be managed at either from the host or vCenter. As with many VMware concepts, they decoupled these components to add more functionality to the environment. The management portion (control plane) can only happen now from vCenter, but the data plane remains on the hosts. So, when you lose vCenter you basically zombie the network till you bring vCenter back… but it will continue to function fully as it was previously configured prior to the failure.
So where is my configuration information stored at? vCenter chooses a location on a shared VMFS within a folder called .dvsData folder. Since it is chosen automatically by vCenter, you can use the
net-dvs
command to find that folder. It will usually be a folder that all vDS enabled hosts have access to. The host also keeps a backup on this configuration database locally at
/etc/vmware/dvsData.db
which is probably only used if vCenter goes down and you also lose connectivity to the shared storage hosting the vDS configuration. This can be very reassuring to know that Virtual Distributed Switches have multiple layers of redundancy and are not fully dependant on vCenter for anything more then initial configuration and management.
I’ve been using vDS for about a year now, and I’ve brought down vCenter many times (for maintenance or otherwise – because we use a physical non-clustered server)… I can assure you that my host networks have never been impacted by this. vDS is very stable and packed with benefit.
