Thursday, August 25, 2011

Could not power on VM : No space left on device - Failed to power on VM

With VMWare's ESX or ESXi, "Could not power on VM : No space left on device - Failed to power on VM" is a common sight when trying to start a VM.

This error seems bizarre especially when you are actually trying to increase the guest RAM and the error is about disk space. The cause could be the following:
  1. By default, ESX will configure a swap on the VM's datastore equal to the RAM. So, when RAM is increased, more disk space is required. The fix is to reserve memory in resource allocation settings for the VM.
  2. There really isn't enough disk space on the datastore. Reduce Hard Disk size for the VM.

6 comments:

  1. Please leave a comment if this post helped you, or if you find something else that fixed your problem. Thanks!

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  3. Thank you! Why is this necessary? Most of my vm's do not have a reservation, yet they are happy...

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    Replies
    1. Thanks for your comment Mark. This post specifically targets the "No space left on device" error when trying to increase the RAM of your existing VM. With this error you have 2 solutions, to rebuild your VM, or to reserve memory. By reserving memory, when RAM is increased, ESX does not require any extra disk space for swap.

      In short, memory reservation is not necessary, but helpful if you want to increase RAM of an existing VM and you do not want the VM (swap) to use more of your valuable disk space.

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