Danstr1
asked on
Witness failure on a 2-node VSAN
I'm currently in the midst of upgrading our server infrastructure. This is for a small company but they'd like as much redundancy as possible. This has led me to explore a 2 -node VSAN as our environment is already VMWare based. I understand that this also requires a a third host serving as a witness. Most of the related documentation I found deals primarily with larger implementations and also discusses what occurs during host failures etc but I've found little that addresses what happens when a witness fails with a simple 2-node implementation. Does the Witness represent a single point of failure? What happens if the Witness is offline/down as there's no redundancy for it in this implementation? Will the servers continue working normally or would it isolate the servers to protect them until the witness is back online? Would any down time be experienced by the users? If things function normally without the witness, what would the time window be to get the witness back online?
The hosts and the witness would all be running locally in a single data center. I've seen where the 2-node approach is often used from branch or remote offices. This wouldn't be the case for us as it represents our "data center." Pursuing the minimum of one more host would provide redundancy for the witness but this isn't feasible financially with the additional hardware and software costs. Basically, I have to weigh the risks of the 2-node or stick with a traditional 2 hosts running on a direct attached SAN.
Thanks in advance!
The hosts and the witness would all be running locally in a single data center. I've seen where the 2-node approach is often used from branch or remote offices. This wouldn't be the case for us as it represents our "data center." Pursuing the minimum of one more host would provide redundancy for the witness but this isn't feasible financially with the additional hardware and software costs. Basically, I have to weigh the risks of the 2-node or stick with a traditional 2 hosts running on a direct attached SAN.
Thanks in advance!
If the witness fails, your hosts will continue normal operation.
You can also just rebuild the witness if you loose if completely ;-)
But you are no longer protected against additional failed hosts/disks, so if another component fails, the cluster can no longer decide which component is authorative without the witness.
For ROBO scenario it is also supported to have the witness in a remote / central datacenter or in the cloud.
With a small 2-node scenario, you could maybe add a 3rd node for backup/recovery (maybe covered by your vSphere Essentials license?) and make this host the witness node.
The witness node can be a physical host (two small local disks required in addition to other storage/datastores on this host, you can not use an existing datastore for this), or hosted as a virtual appliance on another ESXi (the required disks can be placed on a normal datastore on the parent host)
2-node vSAN is mainly attractive if you want to stretch the hosts over two independent server rooms for higher protection against physical damage, and you have only gigabit networking (and you do not want to invest in higher performanece storage networking infrastructure for an iSCSI/Fibrechannel storage). You can just use crossover cables with 10gbit/40gbit/100gbit between the hosts.
But you are right, for small single-serverroom solutions a SAS direct attached storage is maybe more simple solution.
You can also just rebuild the witness if you loose if completely ;-)
But you are no longer protected against additional failed hosts/disks, so if another component fails, the cluster can no longer decide which component is authorative without the witness.
For ROBO scenario it is also supported to have the witness in a remote / central datacenter or in the cloud.
With a small 2-node scenario, you could maybe add a 3rd node for backup/recovery (maybe covered by your vSphere Essentials license?) and make this host the witness node.
The witness node can be a physical host (two small local disks required in addition to other storage/datastores on this host, you can not use an existing datastore for this), or hosted as a virtual appliance on another ESXi (the required disks can be placed on a normal datastore on the parent host)
2-node vSAN is mainly attractive if you want to stretch the hosts over two independent server rooms for higher protection against physical damage, and you have only gigabit networking (and you do not want to invest in higher performanece storage networking infrastructure for an iSCSI/Fibrechannel storage). You can just use crossover cables with 10gbit/40gbit/100gbit between the hosts.
But you are right, for small single-serverroom solutions a SAS direct attached storage is maybe more simple solution.
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https://searchvmware.techtarget.com/tip/Set-up-a-vSAN-2-node-cluster-for-small-or-remote-deployments