The -x (or --check ) option in vmkfstools is used to check the consistency of a virtual disk and, in many cases, repair a disk that has become corrupted or "dirty." This is often the first line of defense when a Virtual Machine (VM) refuses to power on due to disk errors. Primary Use Cases 1. Checking Disk Consistency
In ESXi, sparse disk formats (like thin, delta (snapshot), or eagerzeroedthick) have a structure where metadata tracks which blocks are allocated and where data is stored. If a VM crashes or storage issues occur, this metadata can become inconsistent. vmkfstools -x
You cannot run a check or repair on a disk that is currently attached to a running VM or locked by another process. The -x (or --check ) option in vmkfstools
-X It is common to confuse these two flags, but they serve entirely different purposes: Feature -x (Lowercase) -X (Uppercase) Primary Goal Check or repair disk health Extend/Increase disk size Usage Troubleshooting corruption Adding storage capacity Example vmkfstools -x check disk.vmdk vmkfstools -X 60G disk.vmdk Critical Usage Notes Backup First If a VM crashes or storage issues occur,