How to Expand a VMFS Datastore
An administrator needs to expand a VMFS6 datastore that is currently 2 TB in size. The LUN presented to the ESXi host has been expanded to 3 TB from the storage array. Which command should the administrator use to extend the datastore?
Quick Answer
The answer is `vmkfstools --growfs` because this is the only VMware-supported command to expand a VMFS6 datastore after a LUN resize, as it grows the file system into the newly available unpartitioned space on the device without requiring a new partition or extent. Unlike VMFS5, which could use `fdisk` or `parted` to modify the partition table, VMFS6 strictly requires the `--growfs` flag to directly expand the file system on the existing block device, preserving the original partition layout and avoiding corruption. On the VMware Certified Professional Data Center Virtualization VCP-DCV exam, this question tests your understanding of VMFS6 storage management and the critical distinction between resizing a LUN and expanding the datastore—a common trap is confusing `--growfs` with `--extend` (used for adding a new extent) or attempting to repartition the disk. Remember the memory tip: "Grow the FS, not the partition" — for VMFS6, always use `--growfs` after a LUN resize.
⚠ Common exam trap
Test-takers frequently confuse the `esxcli storage vmfs` commands with the `vmkfstools` commands, mistakenly thinking `esxcli storage vmfs grow` is valid, or they assume `vmkfstools --extend` applies to datastores when it is actually for VMDK files.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
vmkfstools --growfs /vmfs/devices/disks/naa.60050768018603e1b800000000000001
The correct command is `vmkfstools --growfs` because it is the only VMware-supported method to expand a VMFS6 datastore after the underlying LUN has been resized. This command grows the file system to use the newly available unpartitioned space on the device, without requiring a new partition. The `--growfs` option specifically targets the VMFS file system, not the partition, which is essential for VMFS6 datastores.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
esxcli storage vmfs extend -l naa.60050768018603e1b800000000000001
Why it's wrong here
The correct esxcli command is 'storage vmfs extend' but with different syntax.
- ✗
esxcli storage vmfs grow -l naa.60050768018603e1b800000000000001
Why it's wrong here
'grow' is not a valid esxcli command.
- ✗
vmkfstools --extend /vmfs/devices/disks/naa.60050768018603e1b800000000000001
Why it's wrong here
--extend is not a valid option; use --growfs.
- ✓
vmkfstools --growfs /vmfs/devices/disks/naa.60050768018603e1b800000000000001
Why this is correct
This command extends the VMFS datastore to the full LUN size.
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Same concept, more angles
2 more ways this is tested on VCP-DCV
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. An administrator runs vmkfstools on a VMFS datastore and receives the output shown. The datastore is backed by a single LUN from a SAN array. What is the most likely explanation for the multiple extents shown?
medium- A.The LUN was presented to the host with multiple paths, and each path is treated as a separate extent.
- ✓ B.The datastore was expanded by adding an extent from the same LUN.
- C.The datastore is a VMFS6 datastore with three logical volumes aggregated into one namespace.
- D.The virtual machine has a large VMDK file that spans multiple extents due to VMFS6 sub-block allocation.
Why B: When a VMFS datastore is expanded using the same LUN, vmkfstools can show multiple extents because the additional space is added as a separate extent on the same physical LUN. This is a common practice to grow a datastore without reprovisioning a new LUN, and the output reflects the original and expanded extents both pointing to the same LUN identifier.
Variation 2. A vSphere administrator has a VMFS6 datastore that is running low on space. The storage array has additional unallocated LUNs. The administrator attaches a new 2 TB LUN to the ESXi host. What is the correct procedure to increase the datastore capacity?
easy- ✓ A.Use the 'Increase datastore capacity' wizard to add the LUN as an extent
- B.Unmount the datastore, expand the VMFS partition, then remount
- C.Recreate the datastore with a larger block size and restore from backup
- D.Create a new datastore on the LUN and use Storage vMotion to migrate VMs
Why A: The correct procedure is to use the 'Increase datastore capacity' wizard to add the new LUN as an extent to the existing VMFS6 datastore. VMFS6 supports online extension, allowing the datastore to be expanded without unmounting or disrupting running VMs. Option B is incorrect because unmounting and extending the partition is unnecessary; VMFS6 handles this dynamically. Option C is incorrect because recreating the datastore with a larger block size is disruptive and not required—adding an extent achieves the capacity increase. Option D is incorrect because creating a new datastore and migrating VMs is unnecessary and adds complexity; the existing datastore can be extended seamlessly.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This VCP-DCV practice question is part of Courseiva's free VMware certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the VCP-DCV exam.