VM Resource Management

Respurce management in VM:

Memoery  Reservation:
Dedicated amount of pyscial memeory  for a VM all the time.It is the min amount of RAM required for VM to power on. If the reservation is not set vkernal uses Vmkernal Swap rather than the physical memeory which would degrade the performance of VM but the VM is powered on.
Once the memeory is reservered it can not be reclamied or used by other vm's or hypervisor.Only transperent page sharing can be used with memory reservation.
Memory resrvation incsrease SWAP file size decreases.Number of VCPU and Configured memoery determine the overhead.A Host has 4 GB of moeoery and you allocate 1 GB reservation to 4 VM's then you can not overcommit meoery since you have reserved all the memeory.
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Memoery Limit:
The Key problem with the use of memory limits is thta they are enforced without aby guest OS awareness.
If a VM is configured  4GB of RAM guest OS thinks it has 4 GB of RAM and works accordinly .Then if you limit the memory to 2 GB the VMkernal forces the the Limit os 2GB out of 4GB and guest OS thinks it is using all 4GB and thus causing  VM disk swapping and degrades the performce

Bottamline :Vm with less memoery would perform better than VM is more moery and Memory limit.
Memeory Limit is useful in cases when you have limited resources and you want to put a host into maintence mode in such case to limit the reources of VM.

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Memoery Share :
Unlike memory limit and reservation .Memoery share would only come into effect when the ESXi is memoery constraint.VM with more share vlaue would get the preference in such cases.
Some people orgue that memeory share can be achived by memeory reservation yes they are correct but you are commiting the moemeory and thus limiting the number of VM's per host.
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Cpu reservation :
CPU reservation is smiliar to memoery reservation but differ in one accept that memeory reserved can never be reclaimed ,page to disk and shared memmory but CPU reservation can  use idle cpu cycles to other VM's and will be recliamed when the original VM needs it.
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Expandble Reservation in Resource pool :
Allows resource pools to barrow resources from parent host or parent resource pools only to satisfy VM reservations not to stisfy excess resource reservation.

NETIOC - > Net I/O --> DV switch -4.1 -->outgoing
stroage IOC -> datastore should be managed by single Vcenter -- > Latency --- >per disk.