Which HP storage solution best fits the customer requirements?

HP StoreSure is not a standard HP storage product family and does not represent a recognized solution in the HP storage portfolio.

HP StoreVirtual is a VSA-based iSCSI SAN solution designed for virtualization and block storage workloads, not primarily for file serving or document management.

HP StoreAll is a scale-out NAS and object storage platform designed for petabyte-scale big data and archiving workloads, which is over-engineered for a 500-employee law firm's file-serving needs.

HP StoreEasy is purpose-built for network-attached storage workloads such as file sharing and document management, making it the correct fit for a law firm with a document management system and Windows-centric infrastructure. It runs Windows Storage Server and integrates natively with Active Directory, providing the simplicity and manageability appropriate for SMB environments. Its capacity and feature set align with file-serving requirements without the complexity of SAN or scale-out object storage.