Microsoft.RecoveryServices/vaults: sku can't be set to RS0

According to the spec https://github.com/Azure/azure-rest-api-specs/blob/master/specification/recoveryservices/resource-manager/Microsoft.RecoveryServices/stable/2016-06-01/vaults.json, it should be possible to set "sku" to RS0, however when trying to set that I get:

Status=400 Code="InvalidRestApiParameter" Message="sku parameter is invalid.\r\nPlease provide a valid sku"

Another problem is that it isn't documented what the RS0 value actually does. I assume that it sets the storage redundancy type to LRS instead of GRS, but this is nowhere documented. If I change the redundancy portal in the portal, the generated ARM template changes:

from:

"sku": {
"name": "Standard"
},

to:

"sku": {
"name": "RS0",
"tier": "Standard"
},

See also related issue: https://github.com/terraform-providers/terraform-provider-azurerm/issues/2274

Start with specification/recoveryservices/resource-manager/Microsoft.RecoveryServices/stable/2016-06-01/vaults.json and compare its sku definition with the reported 400 response for RS0. Read the related terraform-provider-azurerm issue and the comment thread for the expected service behavior. Done means the specification and documentation accurately reflect whether RS0 is accepted and what it changes.

Written by the indexing model from the issue text.