How much space does a virtual machine need?

[aetius1980]

Assuming I have 100 Windows vms of 40GB each on my datastore, would I need 3.9 TB on my datastore to accomodate all those vms?

I'm guessing not, but how can I find out the actual space requirements?

[Troy_Clavell]

you have to account for the swap file as well.  Each VMs swap file will equal the amount of vRAM presented to each guest.

Also, consider leaving 15 - 20% free space on the LUN for spapshot growth

[weinstein5]

Each VM will need:

• Space for configuration files - this is nominal compared to the 40 GB
  
• Logs
  
• VIrtual Disk - which by default are configured as thick provisioned which means if the machine has a 40 GB physical disk a 40 GB virtual disk file - you could provision as a thin which means the virtual disk will only be as large as the data that is used the challenge with thin provisioning is as the disks grow you can reach a stiaution where you run out of space on your datastore
  
• Per VMkernel Swap FIle - this a page file used by the vmkernel to swap VM memory to when the ESXi host is running out of memory - worst case is it will be equal to the amount of memeory assigned to the VM
  

To accurately assess the amount of space needed you should a tool like VMware Capacity Planner -

[aetius1980]

Seriously?

So if you planned on creating a data store for 100 40GB VMs you'd pre allocate 4TB?

I was thinking of allowing 10% for growth and just going with 5TB (allows for a spare disk as well)

I thought thin provisioning was supposed to reduce the storage demands, but I'm not sure how much I can get away with....

thanks

[Troy_Clavell]

thin provisioning is always an option... You just have to carefully administrate the LUN free space.  10% free space on a LUN that big would be sufficient

[weinstein5]

Are you looking virtualize servers or desktops? If it is desktops then with VMware View you can take dvantage of linked clones where the common files of the OS are stored once and through the use of snapshots each virtual desktop can be unique. This does save on required storage

[aetius1980]

Cheers for the information guys,

VMware architecture is making my head spin in circles !! Help much appreciated 🙂

David,

I wonder if you could help on another question?

As part of the same design, I've got to move a mixture of physical and virtual servers onto to new hosts. I've simply measure peak memory usage over a few days and came up with 320GB, I'm thinking of just providing my new host with 350GB to allow a little room for growth.

I have a combination of servers to move, including SQL and Exchange.

In the absence of the VMware capacity planner is this a safe approach?

Thanks

[weinstein5 · Accepted solution]

That is an appropriate approach.the 320 GB is the memory usage for all the machines  I am assuming the 320 GB is for all the machines you will be virtualizing.

350 GB should be fine however with Exchange and SQL and their abiilty to spike I would consider not cutting it so cloase - maybe looking at 512 GB -  

[aetius1980]

Cheers David, thanks

[Josh26]

40GB

The Windows OS itself can easily burn this much or quite a bit more. A 40GB allocated, thin provisioned disk, which is using 39GB and crashing due to a lack of space is not going to save anything :smileysilly:

I'm surprised you're getting away with such small disks.

[Kahonu84]

Wow... What version of Windows are you using?? We have 60 or so Windows VMs running from XP thru 2k12. I would feel safe in betting 75% of those are running with 25GB of disk or less. And that's with apps loaded.