ESX Datastore sizing and allocation

I have been seeing a lot of activity in the VMTN forums regarding datastore sizing and free space.  That said I decided to write a post about this topic.  There are endless possibilities when it comes to datastore sizing and configurations but I’m going to focus on a few keep points that should be considered when structuring your ESX datastores.

All VM files kept together

In this configuration all VM files are kept together on one datastore.  This includes the vmdk file for each drive allocated to the VM, the vmx file, log files, the nvram file, and the vswap file.  When storing virtual machines this way there are some key considerations that need to be taken into account.  You should always allow for 20% overhead on your datastores to allow enough space for snapshots and vmdk growth if necessary.   When allocating for this overhead you have to realize that when a VM is powered on a vswap file is created for the virtual machine equal in size to the VM’s memory.  This has to be accounted for when allocating your 20% overhead.

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