Short tip: VMware vSphere “Module DiskEarly power on failed to lock file”

While booting a virtualized cluster node I stumped upon a suspicious error message recently:

Module DiskEarly power on failed to lock file

In the VMware forums I found a hint that locking mechanisms might account for this issue. However the thread focussed on desktop products and not on vSphere. I found no lock files (*.lck) on the appropriate datastore so I had a deeper look at the VM configuration file (*.vmx) and discovered the following lines:

ctkEnabled = "TRUE"
scsi0:0.ctkEnabled="true"
scsi1:0.ctkEnabled="true"

In this case Changed Block Tracking (CBT) which cannot be used along with my VM was activated. CBT is used in combination with backup solutions to detect and store only changed blocks of particular VMs to save time and storage capacity. As my affected VMs build a cluster with virtualized storage the feature can’t be used. Configuration this kind of storage prevents using CBT and snapshots which results in an error during boot. To fix this issue I disabled CBT for the affected VMs:

ctkEnabled = "FALSE"
scsi0:0.ctkEnabled = "false"
scsi1:0.ctkEnabled = "false"

Afterwards it was possible to boot the VM again. 🙂

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