High I/O on VM causes clone to fail

When creating a hot clones of VMs that have high I/O you may encounter the following error:

Cannot create a quiesced snapshot because the snapshot 
operation exceeded the time limit for holding off I/O in the 
frozen virtual machine

This is s common issue when trying to perform clones of very busy production servers such as SQL Server or Exchange Server. As these applications perform constant reads/writes the usual quiescing function (when initiating a clone or snapshot  fails to flush all of the operations to disk. Below is an example of this error when trying to hot clone a very busy Exchange server:

A quick and dirty fix if you simply want to clone the VM is to stop the VMware Tools Service on the guest and then re-run the clone. It should complete OK. This basically bypasses the quiescing of the file system and produces a crash-consistent clone:

VMware KB article 1018194 highlights this issue and prescribes various fixes depending on your circumstance.