ESxi 5 cluster HA setting , in 7 ESXi 5 server I kept 1 as a tolerate

[rmustafa]

ESxi-5 cluster HA setting , in 7 ESXi-5 cluster server I kept 1 as a tolerate,

Is it okay to keep , host failure the cluster tolerates: 1 in cluster of 7 ESXi-5 server ???

[Virtualinfra]

Its depending on your need. If you want you can set even 2 host as tolerance.

For example

1.if the cluster is having 7 host and its you have set to 1 host a tolerance, at any given point of time 1 host resource will be kept aside for redundancy incases if any host failure in the cluster.

2. you have 7 host and its is capable of having 10VM each and 1 host is set to tolerance. and cluster has a total of 50 servers and 2 host fails in this scenario then all the VM will power on the available host. but you cant have more than 60 Vm because the tolerance set will reserve 1 ESXi host resource for redundancy incase of HA failure.

3. another scenario take 7 host and capable of have 10VM each and you have 60 VMs in the cluster where it is set to 1 host tolerance and 2 host failed in this scenario. so only 10 VM will be powered on in the available host. and another 10VM will be remained power off due to non availability of the resources.

3. Set tolerance will reserve the host resource from the cluster pool to commit the failure of the host.

Hope this clarifies.

[cjscol]

When using number of hosts a HA cluster toletares then you have to be careful when using reservations on virtual machnes.  This admission control policy works on slots.  The slot size is the size of the largest CPU reservation on any of your virtual machines and the largest memory reservation on any of your virtual machine + virtual machine overhead.  I will ignore virtual machine overhead or now as it makes it easier to explain.  So f you have VM1 with a 1Ghz CPU reservation and a 1GB  memory reservation and VM2 without a CPU reservation but a 2GB memory reservation then your slot size will be 1Ghz CPU and 2GB Memory.  Now if your hosts have 2 x quad core 3Ghz processors and 64GB of memory then they will have a total of  24Ghz CPU (2 CPU x 4 cores x 3Ghz) and 32GB memory, so they will have 24 slots, i.e. 24Ghz and 48GB memory (24 slots x 2GB).  Yes you have more memory than this put each slot also requires 1Ghz and there is no more processing power. If you tolerate 1 host failure then you can run a maximum of 144 virtual machines (6 x 24) before HA will stop you powering on more virtual machines.

The number of virtual machines you can power on will depend on your slot size.  Remember this admission control policy works off your largest virtual machines and assumes all virtual machines may require the same.  Using a percentage admission control policy works off what each virtual machines is actually configured for and may be a better solution for you.