MICDROP
Enthusiast
Enthusiast

Does an VMFS 6 (Auto UNMAP) require SDELETE to work?

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Hi, all.

I have a question while studying about Reclaim.

I understand that erasing data from a VM will only delete index files and not delete data from storage blocks.

So, in fact, to reduce the size of the vmdk file, we saw that after sdelete on Windows, you would need to use vmkfstool to perform UNMAP on ESXi.

1. Do I have to do UNMAP on the storage side after this? (Because data is actually stacked on storage blocks.)

2. Does the vSphere 6.5 (VMFS6) support Auto UNMAP, which means that Windows does not need to perform sdelete?

Thank you in advance for your advice.

Regards.

1 Solution

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Lalegre
Virtuoso
Virtuoso

Hey MICDROP​,

From Windows 2012 the UNMAP capability is enabled by default which means that if the VM is placed in an datastore with VMFS6 format, the ESXi will instruct the array to automatically reclaim the unused space.

Take into account that UNMAP will work with sizes greater than 1 MB and with blocks only aligned with 1 MB, if it is not like that, UNMAP simply will not work. SDELETE was used for Windows Server 2008 r2 to run the UNMAP operations manually.

I suggest you to go over the next section which is not to long and will give you a quick understanding about the configuration and limitations: Space Reclamation Requests from VMFS Datastores

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Lalegre
Virtuoso
Virtuoso

Hey MICDROP​,

From Windows 2012 the UNMAP capability is enabled by default which means that if the VM is placed in an datastore with VMFS6 format, the ESXi will instruct the array to automatically reclaim the unused space.

Take into account that UNMAP will work with sizes greater than 1 MB and with blocks only aligned with 1 MB, if it is not like that, UNMAP simply will not work. SDELETE was used for Windows Server 2008 r2 to run the UNMAP operations manually.

I suggest you to go over the next section which is not to long and will give you a quick understanding about the configuration and limitations: Space Reclamation Requests from VMFS Datastores

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MICDROP
Enthusiast
Enthusiast

Thank you very much for your accurate answer!

Can I know a little more about Windows version that automatically performs SDELETE? Does Window 10 also perform SDELETE automatically?

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Lalegre
Virtuoso
Virtuoso

Hey,

I checked in my Windows 10 laptop using the next Powershell command:

Get-ItemProperty -Path "HKLM:\System\CurrentControlSet\Control\FileSystem" -Name DisableDeleteNotification

If the value is 0 it means is already enabled and SDELETE is a utility that was used in the past when UNMAP was not an in-guest feature for Windows Server and also Windows Desktop. So regarding to your question, yes, Windows 10 will perform UNMAP automatically.

I would suggest you however to ask into the Microsoft forums to get more deep about the support, limitation and requirements.

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MICDROP
Enthusiast
Enthusiast

Value is 0 on my laptop too! (Windows 10)

Below is a summary of the conditions for Auto UNMAP to work with VMFS6.

1. vSphere 6.5 or later (VMFS 6)

2. Block size is 1 MB or greater than 1 MB

3. OS with auto UNMAP enabled

Is there something I misunderstood?

I learned some really important information because of you!

Thank you for your reply.

Lalegre
Virtuoso
Virtuoso

You understood everything, those are the basic requirements for it to work!

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depping
Leadership
Leadership

Well, your storage array will also still need to support UNMAP for it to work of course... You can check if the array supports it via the command listed in this KB: VMware Knowledge Base

loungehostmaste
Enthusiast
Enthusiast

why would the storage array need to support UNMAP when it's about "punch holes" in the sparse files on the VMFS?

given that fstrim from a linux guest on a nested ESXi on top of VMware workstation works perfectly i strongly doubt that
yes, the growable vmdks hosting ESXi don't and can't shrink but that doesnt matter for reclaim on the VMFS in the middle

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