Vmware Reservation vs Shares
Vmware Reservation vs Shares
If I understand when you have for instance 2 VMs :
VM1 = Memory Reservation : 3 GB , CPU : 1GHZ
VM2= Memory Reservation : 4 GB , CPU: 2GHZ
Now whatever Share you allocate to VM1 or VM2, it is not going to make any difference , since VM1 and VM2 will have Memory and CPU guaranteed as allocated above.
So how does the Share work in comparison to Reservation ?
Thank you
If I understand when you have for instance 2 VMs :
VM1 = Memory Reservation : 3 GB , CPU : 1GHZ
VM2= Memory Reservation : 4 GB , CPU: 2GHZ
Now whatever Share you allocate to VM1 or VM2, it is not going to make any difference , since VM1 and VM2 will have Memory and CPU guaranteed as allocated above.
So how does the Share work in comparison to Reservation ?
Thank you
I recommend you to check Reservations and Shares explained in this document on page 3.
https://www.vmware.com/content/dam/digitalmarketing/vmware/en/pdf/techpaper/performance/drs-cluster-mgmt-perf.pdf
Some examples:
https://4sysops.com/archives/understanding-vsphere-shares-reservations-and-limits/
https://www.vmware.com/content/dam/digitalmarketing/vmware/en/pdf/techpaper/performance/drs-cluster-mgmt-perf.pdf
Reservation
Reservation is a way of guaranteeing resources for a VM. When the user reserves resources for a VM, they are asking the host to make sure the VM always gets the reserved resources. The reservations set are static, which means that the VM is entitled to these resources whether it uses them or not. For this reason, resources reservations for a VM will have a multi-dimensional impact.
Shares
Shares dictate the relative priority of resources for a VM, compared to resources of other child objects (siblings) of the same parent. The absolute number does not matter in shares, as the values are always relative. For example, if three VMs of the same resource pool have shares set to 16000, 8000 and 4000, the resources are distributed among the VMs in the ratio of 4:2:1 respectively.
Some examples:
https://4sysops.com/archives/understanding-vsphere-shares-reservations-and-limits/
ASKER
in my example above:
VM1 = Memory Reservation : 3 GB , CPU : 1GHZ
VM2= Memory Reservation : 4 GB , CPU: 2GHZ
to make it simple let 's say we have one ESX that has 7GB RAM and 3GHZ CPU
Now if you give VM1 Shares 10000 and VM2 500, then if VM1 needs more memory , it cannot get any more than 3 GB, even though it has more Shares than M2
VM1 = Memory Reservation : 3 GB , CPU : 1GHZ
VM2= Memory Reservation : 4 GB , CPU: 2GHZ
to make it simple let 's say we have one ESX that has 7GB RAM and 3GHZ CPU
Now if you give VM1 Shares 10000 and VM2 500, then if VM1 needs more memory , it cannot get any more than 3 GB, even though it has more Shares than M2
Correct because you've defined the VM memory settings to 3GB.
Memory is not dynamic....it cannot grow above what has been defined....
What would the OS make of having it's memory map change in real time....
Memory is not dynamic....it cannot grow above what has been defined....
What would the OS make of having it's memory map change in real time....
ASKER
So it sounds to me Reservation and Shares are Exclusive.
If you have Reservation for a VM, then the VM will not start unless if it meets the condition of the Reservation.
Shares will apply for VMs that do not have Reservation set up..
Please correct me where I am wrong
If you have Reservation for a VM, then the VM will not start unless if it meets the condition of the Reservation.
Shares will apply for VMs that do not have Reservation set up..
Please correct me where I am wrong
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ASKER
Thank you Guys!
I will come back to this topic.. as I am not really clear on it.
I will come back to this topic.. as I am not really clear on it.
Shares only work when contention occurs.
It's a priorty option for CPU and Memory.