Thanks in advanced for your help.
My first question is about DRS. After configuring DRS and HA, if the Virtual Center is down for a couple of hours, is DRS and HA fully operational even if VC is down.
My second question is about deploying a template. Is VC involved in copying the template image, meaning that the image travels to VC and back to a VMFS volume. Or is it ESX that performs the image transfer.
My third question is about HA. Is it possible to have a redondant network path for HA so that if the console network segment goes down, HA would rely on another network segment to get hearbeat from other hosts.
My forth question, still about HA. If the network segment for the VMs, goes down, thus rendering the VMs inaccessible to clients, those HA detects that and relocates the VMs to another host.
Thanks
Richard.
Hi
1. i disagree on that one piacas , HA will continue to function when VC is down, the configuration is stored locally on each ESX in the Cluster. DRS will stop functioning with out VC.
2. no it is only travelled between ESX server.
3. yes you can create a second SC port on a diffrent LAN or put the SC on a NIC Team.
4. NO, if the network for the VM's goes down it wont affect HA
Niran E.C
1. VC is needed for HA and DRS, so when VC is down, they won't function.
2. Its only involved in that it will update the DB knowing you have a template. The actual copy will happen from ESX over the fiber.
3. yes, can have multiple console links or multiple NIC tied to console switch.
4. Good question..I believe it does, but not sure......
Hi
1. i disagree on that one piacas , HA will continue to function when VC is down, the configuration is stored locally on each ESX in the Cluster. DRS will stop functioning with out VC.
2. no it is only travelled between ESX server.
3. yes you can create a second SC port on a diffrent LAN or put the SC on a NIC Team.
4. NO, if the network for the VM's goes down it wont affect HA
Niran E.C
I agree with Niranec
I agree with Niranec too.
It definitely will, the ESX servers heartbeat each other as well as the Virtual Center server.
How does VMware HA work?
VMware HA continuously monitors all ESX Server hosts in a cluster and detects failures. An agent
placed on each host maintains a "heartbeat" with the other hosts in the cluster and loss of a
heartbeat initiates the process of restarting all affected virtual machines on other hosts.
You create and manage clusters using VirtualCenter. The VirtualCenter Management Server
places an agent on each host in the cluster so each host can communicate with other hosts to
maintain state information and know what to do in case of another host's failure. (The
VirtualCenter Management Server does not provide a single point of failure.) If the VirtualCenter
Management Server host goes down, HA functionality changes as follows. HA clusters can still
restart virtual machines on other hosts in case of failure; however, the information about what
extra resources are available will be based on the state of the cluster before the VirtualCenter
Management Server went down.
Host failure detection occurs 15 seconds after the HA service on a host has stopped sending heartbeats to the other hosts in the cluster. A host stops sending heartbeats if it is isolated from the network. At that time, other hosts in the cluster treat this host as failed, while this host declares itself as isolated from the network.
By default, the isolated host powers off its virtual machines. These virtual machines can then successfully fail over to other hosts in the cluster. If the isolated host has SAN access, it retains the disk lock on the virtual machine files, and attempts to fail over the virtual machine to another host fails. The virtual machine continues to run on the isolated host. VMFS disk locking prevents simultaneous write operations to the virtual machine disk files and potential corruption.
If the network connection is restored before 12 seconds have elapsed, other hosts in the cluster will not treat this as a host failure. In addition, the host with the transient network connection problem does not declare itself isolated from the network and continues running.
In the window between 12 and 14 seconds, the clustering service on the isolated host declares itself as isolated and starts powering off virtual machines with default isolation response settings. If the network connection is restored during that time, the virtual machine that had been powered off is not restarted on other hosts because the HA services on the other hosts do not consider this host as failed yet. As a result, if the network connection is restored in this window between 12 and 14 seconds after the host has lost connectivity, the virtual machines are powered off but not failed over.
VMware HA monitors heartbeat between hosts on the console network for failure
detection. So, to have reliable failure detection for HA clusters, the console network should have
redundant network paths. That way, if a host's first network connection fails, the second
connection can broadcast heartbeats to other hosts. To set up redundancy, you need two
physical network adapters on each host. You then connect them to the corresponding service
console, either using two service console interfaces (each on a separate vSwitch or a separate
physical network adapter) or using a single interface with NIC teaming.
Here's some white papers on each...
http://www.vmware.com/pdf/vmware_ha_wp.pdf
http://www.vmware.com/pdf/vmware_drs_wp.pdf
This is a good guide also...
That pretty well answers question 1 to 3. About question 4 and HA, If I understood correctly, HA only verify the availability of ESX servers and if a network card in ESX, associated to a virtual switch used by VMs, lose network signal, HA doesn't detect that.
you have two scenarios with HA:
1. the server has crashed, if it did then the VM's will start on the other ESX servers .
2. one server has become isolated, which means that the SC network is down. in this case it will do what you configured in the HA policy (Restart VM's on othr ESX server or keep them allive) this will be done after the ESX will check to see if his network is down or all the other server in the cluster has crashed by pinging the default gateway.
in no scenario there will be a restart of the VM's on another ESX server if the VM network is down.
That is correct, to overcome that you can add multiple NIC's to your vswitch so if one fails the VM's still have connectivity.
Thank you all for your help. You know your stuff!