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Due to various reasons a VSA cluster member might stop responding even though the ESXi host is still working as expected.
So you need to restart services.
thanks for your reply .
Then advise me to manually restart the services on the server where running vsphere client?I must before turn off the virtual machine?
On a 2node VSA this is a problem that can occur.
If you didn't put the VSA cluster in maintenance-mode before rebooting, your VSA service is going to try to find nodes that aren't there.
The problem doesn't occur on a 3node cluster.
On your vCenter server, go to services, find the VSA-services en restart it.
If it doesn't find the nodes again, try to put the VSA-cluster in maintenance 1th & turn it back on again. It takes a while for your cluster to go back online, because of resync etc. Give it time. In your tasks section you should see a message like : "VSADsX resync in progress" or similar. Even if you don't see the message the resync CAN be running in the background. (see the basic manual on vmware, it's all there, it's the 5.1, but it's similar for 5.5. VMware vSphere 5.1)
If you have VM's running, the process is going to be slowed down even more. As with any RAID system, you should avoid using the discs during rebuild excessively, since the rebuild is running