Amazon FSx for Windows File Server supports Multi-AZ file systems in the US West (N. California) Region

You can now create Amazon FSx for Windows File Server Multi-AZ file systems in the US West (N. California) Region to support your business-critical workloads that require highly available shared storage deployed across multiple AWS Availability Zones (AZs), including SQL Server database workloads and line-of-business workloads such as banking, retail, and healthcare applications.

Source:: Amazon AWS