Vsphere 6.5 Slot Size
- Extend Disk / HDD space of Guest OS in ESXi 6.5: In this quick and simple tutorial I will guide you through how to Extend Hard disk space of Guest OS in Vmwa.
- VMware HA Slot is the default admission control option prior to vSphere 6.5. Slot Size is defined as the memory and CPU resources that satisfy the reservation requirements for any powered-on virtual machines in the HA cluster.This article is just to cover how the HA slots are calculated step by step not more than that.
- Often referred to in the virtual community as the vSphere Resource kit, the Host Resource Deep Dive zooms in on hardware resources such as CPU and Memory and covers how the vSphere 6.5 resource scheduler manages these. The Clustering Deep Dive builds on top of that and zooms in how a group of ESXi hosts work together and provide clustering.
When vSphere 6.5 was announced I was quite impressed about the features. Gathering more and more hands-on experience so far I am more than happy with it.
One of the new features that can have a real operational benefit hasn’t been documented so far that often (or at least I haven’t seen it anywhere).
Before vSphere 6.5 it was impossible to increase the VMDK size of a DISK that was larger than 2TB when the Virtual Machine was powered on. That was a fact that not many organizations were aware of it until they stumbled upon it.
Define host failover capacity by HA Slot Policy. You can also have option to choose “Slot Policy”. This is the default option prior to vSphere 6.5. Slot Size is defined as the memory and CPU resources that satisfy the reservation requirements for any powered-on virtual machines in the HA cluster. You have 2 options under Slot Policy.
From an architectural point of view there shouldn’t be many use cases where such a large disk layout would be the best practice. But from an operational point of view for many of my customers this has been a bigger issue.
The good thing is: With vSphere 6.5 this is not the case anymore. Important: Hardware Version 13 (vHW 13) is not required for this to work – therefore just the vSphere platform and not the VM has to be upgraded.
Increasing a hard disk from 2.4 to 3TB will just work while the VM is powered on.
Voila. The disk can be used within with the fully size without any service interruption. Quite cool isn’t it?
Another quite useful enhancement within vSphere 6.5 is the fact that we can now see details about the hardware customization within the events. While in the pre vSphere 6.5 era we were only able to see that a configuration of the VM took place we see now more details about this VM configuration task.
Vsphere 6.5 Slot Size Chart
Just select reconfiguration event in Host & Clusters or VMs & Templates: VM -> Monitor -> Events
The first bigger vSphere 6.5 update must be around the corner. So I would recommend you to plan the upgrade. Check out my blog post about the general design considerations and tasks to be done before upgrading the vCenter.
By Duncan Epping, Principal Architect, VMware
Vsphere 6.5 Ha Slot Size
Yesterday I received a question on twitter:
Hi, to settle an argument in the office, if no reserves are in place, does number of vCPU’s affect slot size in vSphere 4? Thx 🙂
First of all, what is a slot? The availability guide explains it as follows
A slot is a logical representation of the memory and CPU resources that satisfy the requirements for any powered-on virtual machine in the cluster.
In other words a slot is the worst case CPU and Memory reservation scenario for any given virtual machine in a cluster. This slot is used when Admission Control is enabled and “Host Failures Tolerates” has been selected as the admission control policy. The total amount of available resources in the cluster will be divided by the slot size and that dictates how many VMs can be powered on without violating availability constraints. Meaning that it will guarantee that every powered on virtual machine can be failed over.
As said this slot is dictated by the worst case reservation for CPU and Memory. Prior to vSphere 4.0 we used the number of vCPUs to determine the slotsize for CPU as well. But we do not use vCPUs anymore to determine the slot size for CPU. The slotsize for CPU is determined by the highest reservation or 256MHz (vSphere 4.x and prior) / 32MHz (vSphere 5) if no reservation is set.
However, vCPUs can have an impact on your slot… it can have an impact on your memory slotsize. If no reservation is set anywhere HA will use the highest Memory Overhead in your cluster as the slot size for memory. This is where the amount of vCPUs come in to play, the more vCPUs you add to a virtual machine the higher will your memory overhead be.
I guess the answer to this question is: For CPU the number of vCPUs does not impact your slotsize, but for memory it may.