VMware vSphere

Normally swap file is created when you will power on the VM and deleted when you will power off the vm so why .vswp is available for the overhead memory and normally overhead memory is from the physical memory and what would be the total size of RAM for a VM. Is that Allocated + Overhead ? Plz reply me if anyone know this

If you make reservations for your virtual machine's that are equal to the amount of RAM assigned to them, swapping and page sharing does not occur. You can over commit pretty heavily if you are comfortable with poorer performance. If you do not set reservations, ESX host creates a .vswp file equal to the difference between the amount of physical memory assigned to the virtual machine and the reservation it has. By default, memory reservations are set to 0. If you have a virtual machine with 2GB of memory without a reservation, it creates a 2GB .vswp file when it is powered on. The virtual machine starts using the .vswp file if the server is out of physical RAM. If you set a 1GB reservation, it creates a 1GB.vswp file. The .vswp files are what allows for memory overcommitment.

from Verifying sufficient free disk space for an ESX/ESXi virtual machine

Hey i am asking this in context of ESXi5

Look at the list of products in the above link, it contains ESXi 5.0.

This behavior is typical for many VMware products

Do you know there are two .vswp files in esxi5 i am asking about the overhead .vswp file.

Yes second file which named as  vmx-<vmname-tmpstr>.vswp a new file in ESXi 5 and is used by the vmkernel Memory Overhead that exist for each VM - in addition to the actual vRAM configured for the VM to use. This files holds some backing space needed for the Memory Overhead and reduces the amount of actual allocated extra RAM needed for each started virtual machine.

Addionally take a look at vSphere 5.0 New .vswp file & Storage Tax on VDI

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.vswp files in vsphere5

To clarify a bit, vswp file size is usually the size of the configured vRAM of a VM, plus overhead, minus any memory reservation (reserved memory is always backed by physical RAM.)

The amount of overhead required depends on two things:

1. Number of vCPU added to the VM.

2. Amount of vRAM added to the VM.