Storage migration to reduce disk sizes by changing disks from Thick to Thin

[JDMils_Interact]

I have a 24TB server with Thick provisioned Eager Zero disks however only about 4TB is being used. In my vCenter 6.7u3n, I can storage Migrate the server to a new SAN, and can Thin provision the disks in the process to achieve my goal of migrating the server to the new SAN, however, my question is, will the time taken to perform the storage migration be quicker when converting the disks from Thick to Thin or will it take the same time as migrating the server to new storage and keeping the disks as Thick?

This is within the same vCenter, from one SAN to a newer SAN.

My other option may be to use VMware converter to migrate the disks from Thick to Thin in the background and then "flick the switch" when we are ready to complete the move.

[sjesse]

Migrating doesn't always convert to thin, the datastores need to have different block sizes for that to happen

https://kb.vmware.com/s/article/2004155

[nachogonzalez]

I am not entirely sure if doing a svMotion will help you in that case. Mostly because you are using Thick Provisioning Eager Zero, so all the blocks are Zeroed at the moment of provisioning, in that case, I'm not completely sure if they can be reclaimed.
If that works. a 24TB for sure will take a while. But everything depends on the Speed of your SAN (HBA speed, SAN Switches speed, current load, etc)

Hope that works.

[a_p_]

The first question I have after reading your question is what kind (vendor/model) of storage system you are going to use as the target?
Does this storage system support thin provisioning on the storage level? If it does, I'd consider to keep VMs thick provisioned, and do the thin provisioning on the storage side only.

André

[JDMils_Interact]

Both storage units are NetApp, however there is no replication setup between the 2. They both support Thin Provisioning.

[sjesse]

I wouldn't worry about thin provisioning then, with all the compression features netapp has in oncommand your not saving any space other than whats reported in vmware.

[JDMils_Interact]

I've setup VMware Converter and run my first test and the 9TB server took around 24 hours to migrate from old datastore to new and the new disks are now marked as thin-provisioned.

Thanks to everyone for your help.