VM usage of big storage

[sys]

I have an issue with my one of VMs: 

The VM has been provisioned with a 4.6TB hard disk. On the Vmware interface ( on Vcenter), it shows that the storage used is 4.24TB. however, when I check inside the guest OS, the actual disk usage is 2.9TB. So, my current issue is: although the VM is using 2.9TB out of 4.6TB at the guest OS level, vmware report that's 4.24TB out of 4.6 TB.

[Shen88]

@sys,

Please note, This kind of discrepancy between VMware-reported storage usage and guest OS disk usage is actually quite common-especially when using thin-provisioned disks. When a VM writes data, the virtual disk file (.vmdk) grows. But when data is deleted inside the guest OS, the space is marked as free within the OS, not necessarily released back to the underlying storage. Also note, If your VM has snapshots, they can inflate the reported usage significantly.

------------------------------
If you find this answer right, please 'Recommend' this post.

Thank you!

Regards,
Shen
------------------------------

[sys]

@Shen88 Thanks for your information. I understand that: When deleting data in the operating system → that space is marked as "free" in Windows, but not automatically returned to the datastore. So I need to reclaim space on Datastore to solve this issue, right? 

Thank you!

[Alexandru Capras]

Actually, the VMDK is created with the type "Thick Provision Lazy Zeroed", which means the full size of the disk is allocated upfront on the datastore. For example, if you create a 1TB VMDK, 1TB will be immediately reserved on the datastore, even if the guest OS only uses a small portion of it.
Inside the OS, you'll only see the used filesystem space, but from a storage perspective, the entire 1TB is blocked out.

If you want to consume only the space actually written to, you should use "Thin Provision". With thin provisioning, you can assign a virtual disk, let's say of 1TB, but the datastore will only consume what is actually written by the VM - e.g., 200GB if that's all the VM uses. But you need to keep in mind that the VM can claim its full allocated space and start writing data up to 1TB. Thin provisioning can easily lead to over-provisioning your datastore, and imagine what would happen if all thin-provisioned VMs started to consume their full allocated space at the same time.

[Shen88]

Yes, you are right. You need to reclaim space on the datastore. For modern setups with compatible guest OS, VM hardware, ESXi, and storage, this process is largely automated via UNMAP.

------------------------------
If you find this answer right, please 'Recommend' this post.

Thank you!

Regards,
Shen
------------------------------

[sys]

@Shen88 I can do as this article, right? Reclaiming disk space from thin provisioned VMDK files when ESXI Host still sees blocks even after removed from GuestOS