VSAN-Troubleshooting-Reference-Manual

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Diagnostics and Troubleshooting Reference Manual – Virtual SAN Introduction to Virtual SAN Networking Before getting into network in detail, it is important to understand the roles that nodes/hosts can play in Virtual SAN. There are three roles in Virtual SAN: master, agent and backup. There is one master that is responsible for getting CMMDS (clustering service) updates from all nodes, and distributing these updates to agents. Roles are applied during cluster discovery, when all nodes participating in Virtual SAN elect a master. A vSphere administrator has no control over roles. A backup node will assume the master role should the master fail. This will avoid a complete rediscovery of every node, object and component in the cluster, as the backup role will already have a full copy of the directory contents, and can seamlessly assume the role of master, speeding up recovery in the event of a master failure. There are a number of distinct parts to Virtual SAN networking. First there is the communication that takes place between all of the ESXi hosts in the Virtual SAN cluster, indicating that they are still actively participating in Virtual SAN. This is done via multicast traffic, and a heartbeat is sent from the master to all hosts once every second to ensure they are still active. There is also communication between the master and the backup and agent nodes, where the master keeps the other nodes up to date with regards to the configuration of the cluster. This is also multicast traffic, but is relatively light from a traffic volume perspective. Lastly, there is virtual machine disk I/O. This makes up the majority of the traffic on the Virtual SAN network. VMs on the Virtual SAN datastore are made up of a set of objects. These objects may be made up of one or more components, for example a number of RAID-1 stripes or a number of RAID-0 mirrors. Invariably, a VMs compute and a VM’s storage will be located on different ESXi hosts in the cluster. It may also transpire that if a VM has been configured to tolerate one or more failures, the compute may be on node 1, the first RAID-0 mirror may be on host 2 and the second RAID-0 mirror could be on host 3. In this case, disk reads and writes for this virtual machine will have to traverse the Virtual SAN network. This is unicast traffic, and forms the bulk of the Virtual SAN network traffic. V M W A R E S T O R A G E B U D O C U M E N T A T I O N / 96
Diagnostics and Troubleshooting Reference Manual – Virtual SAN Virtual SAN network requirements In this section, the network requirements for Virtual SAN are discussed. Physical Network Interface Card (NIC) requirements VMware will support both 1Gb Network Interface Cards (NICs) and 10Gb Network Interface Cards for Virtual SAN traffic. If 1Gb NICs are planned, VMware recommends that the NIC be dedicated to Virtual SAN traffic. If 10Gb NICs are planned, VMware supports sharing that NIC with other VMware network traffic types (management, vMotion, etc.). Virtual SAN also supports NIC teaming for availability purposes, but be aware that Virtual SAN does not balance Virtual SAN traffic across NICs. NIC teaming is only supported in active/standby mode on the Virtual SAN network. Virtual SAN traffic – vmknic requirement Each ESXi host that wishes to participate in a Virtual SAN Cluster must have a VMkernel interface created [vmknic], and this interface must be configured for Virtual SAN Traffic. This can easily be done and checked via the vSphere web client. For version 5.5, VMware recommends that the Virtual SAN traffic be isolated to a layer 2 non-routable VLAN. Verify that each of the VMkernel ports used for Virtual SAN traffic are on the same subnet, have the same subnet mask and are on the same VLAN segment. In version 6.0, VMware supports Virtual SAN traffic over a layer 3, routable network. A good test to verify that the hosts are able to communicate to each other over this network is to use the vmkping command and have each of the hosts in the cluster ping each other. If this fails to work, the network configuration must be revisited and rechecked on all hosts, and there should be no attempt to enable Virtual SAN until the networking is configured and working correctly. Virtual switch requirement Virtual SAN works with both the original standard switch (VSS or vSwitch) and also with the distributed virtual switch (DVS). Virtual SAN also includes a license for distributed switches, which normally requires an Enterprise+ license edition. This means that customers can take advantage of simplified network management provided by the vSphere Distributed Switch for their Virtual SAN storage regardless of the underlying vSphere edition they use. V M W A R E S T O R A G E B U D O C U M E N T A T I O N / 97
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