Identify the missing word(s) in the following sentence within the context of Microsoft Azure. Zone-redundant configuration for the [..?..] tier has two layers: A stateful data layer with the database files (.mdf/.ldf) that are stored in ZRS(zone-redundant storage). Using ZRS the data and log files are synchronously copied across three physically isolated Azure availability zones. A stateless compute layer that runs the sqlservr.exe process and contains only transient and cached data, such as the tempdb and model databases on the attached SSD, and plan cache, buffer pool, and columnstore pool in memory. This stateless node is operated by Azure Service Fabric that initializes sqlservr.exe, controls health of the node, and performs failover to another node if necessary. For zone-redundant serverless and provisioned General Purpose databases, nodes with spare capacity are readily available in other Availability Zones for failover.