If you are getting this error when you try to expand your storage spaces Vdisk, and you are using StorageTiers.
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error extending volume size not supported storage spaces
you can expand your volume by using powershell instead
run the following command to get the names of your StorageTiers
Get-VirtualDisk <Vdisk FriendlyName> | Get-StorageTier | Select FriendlyName
In my case the name is VeeamVolume
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Get-VirtualDisk “VeeamVolume” | Get-StorageTier | Select FriendlyName
and then expand the desired StorageTier
Get-StorageTier <StorageTier FriendlyName> | Resize-StorageTier -Size <Size>
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Get-StorageTier VeeamVolume_HDD_Tier | Resize-StorageTier -Size 50TB
and after the resize
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after StorageTier Resize
source: https://docs.microsoft.com/en-us/windows-server/storage/storage-spaces/resize-volumes