Historically, many organizations with on-premises infrastructure have relied on boot-from-SAN (Storage Area Network) strategies instead of local storage solutions. Booting from a SAN provides centralized management and backup of boot volumes, supports high availability through multipathing, and offers flexibility by allowing systems to boot from pre-configured OS images on a shared storage array, ultimately reducing costs.
Amazon FSx for NetApp ONTAP brings these advantages to the cloud. As a fully managed service from Amazon Web Services (AWS), FSx for ONTAP offers a virtualized, enterprise-class storage solution equipped with features such as high-throughput I/O, deduplication, compression, compaction, replication, and block-level access via iSCSI and NVMe/TCP. A crucial feature for SAN booting is thin cloning. FSx for ONTAP allows a single thinly provisioned LUN to act as the base “golden image” for an operating system (OS). Read-write snapshot clones of this LUN can be swiftly provisioned and presented to hundreds of servers as individual boot volumes, with each clone only storing the minimal differences that define a server’s identity. This method significantly reduces overall storage requirements. Additionally, FSx for ONTAP’s built-in awareness of shared data regions allows frequently accessed blocks to be cached once in memory and served to all clones, effectively enlarging the apparent cache size and boosting performance. With high availability and disaster recovery (HA/DR) capabilities through advanced replication, boot volumes can seamlessly integrate into HA/DR workflows, ensuring consistent OS states across environments without manual intervention.
One of the main challenges with SAN booting has been the need for specialized boot firmware or host bus adapters, which are often not available in cloud setups. But imagine achieving the advantages of SAN booting without needing specialized hardware. In the sections that follow, we will illustrate how to do just that.
Understanding AWS Boot Devices
Typically, AWS instances boot from Amazon Elastic Block Store (Amazon EBS) volumes, which are closely integrated with Amazon Elastic Compute Cloud (Amazon EC2). This integration allows for quick and reliable boot times, leveraging features like EBS Fast Snapshot Restore and EBS Provisioned IOPS for volume initialization. Amazon EBS also enhances security with customer-managed key (CMK) encryption, provides high resiliency with independent boot volumes, and offers time-based AMI copies for efficient distribution across Regions. Designed for both general-purpose and high-performance workloads, Amazon EBS serves as the default boot device for Amazon EC2.
In this article, we illustrate how you can boot from iSCSI LUNs hosted on FSx for ONTAP file systems—whether in Single-Availability Zone (AZ) or Multi-AZ configurations. These LUNs can be thinly provisioned, space-efficient, and replicable across AZs or AWS Regions.
When configured correctly, SAN booting from FSx for ONTAP can help minimize storage costs at scale while simplifying HA/DR operations.
We will delve into the two primary use cases for SAN booting with FSx for ONTAP, walk through the technical boot process, demonstrate working examples in both Linux and Windows environments, and share best practices for successful implementation in production settings.
Reducing Boot Volume Costs
In on-premises setups, SAN booting is frequently utilized to cut costs when deploying numerous servers with similar boot volumes. The same principle is applicable in the cloud with iSCSI boot using FSx for ONTAP. By employing thin provisioning and snapshot-based cloning, the storage capacity needed for 100 to 200 boot volumes can be reduced to nearly that of a single boot volume. Each server utilizes space only for its unique differences from the golden image, significantly minimizing overall storage consumption. Moreover, by adhering to the best practices outlined later in this post, you can avoid the need for dedicated IOPS for boot volumes, thanks to the performance pooling capabilities of FSx for ONTAP. This results in considerable cost savings with minimal performance impact.
Streamlined HA/DR and OS Lifecycle Management
Operating system updates and configuration changes are ongoing necessities for enterprise workloads. SAN booting simplifies HA/DR by replicating boot volumes across AZs and remote AWS Regions. FSx for ONTAP supports multi-AZ and long-distance replication, ensuring that any changes to the OS or boot volume are automatically synchronized and made highly available. This reduces manual recovery steps and lowers the risk of human error, making it easier to meet strict Recovery Time Objectives (RTOs). Additionally, updates can be staged on a clone of the golden image, thoroughly tested, and promoted to production only after validation, thereby reducing disruption during the OS update process.
How to SAN Boot from FSx for ONTAP Volumes
To boot from FSx for ONTAP, we use a network-based chain-loader boot device, sometimes referred to as a “jumpboot.” The EC2 instance initially boots a compact, locked-down OS image from a 1 GB EBS volume containing a Preboot eXecution Environment (iPXE). This iPXE environment then chain-boots to a volume storing the actual Linux or Windows OS image on FSx for ONTAP. You can compile your own iPXE Amazon Machine Image (AMI) or use an AWS-certified iPXE AMI available in every AWS Region as a community AMI. Chain-loading the OS allows continued use of Amazon EC2 console integration for launch, and start/stop operations like the serial console. But how does iPXE know which FSx for ONTAP and iSCSI volume to boot from? When starting the EC2 instance with the iPXE AMI, we provide this information in the user data script, which iPXE then uses to chain-load the new OS located on the specified block volume. For instance, a SAN-booted EC2 instance running Linux is illustrated in Figure 2, while a Windows instance is shown in Figure 3.
Practical Considerations and Best Practices
Booting from SAN using FSx for ONTAP in AWS entails planning and operational considerations similar to traditional on-premises SAN environments, along with some cloud-specific best practices.
One critical aspect is addressing operating system licensing. Since boot volumes are often cloned, each instance must adhere to its respective licensing requirements—especially for commercial operating systems like Microsoft Windows.
Storage placement is also vital. Unless another specific need arises, it is advisable to place both the boot and data volumes for a given EC2 instance on the same FSx for ONTAP file system. This ensures optimal data locality and consistent performance.
Another recommended practice is to prevent overloading a single FSx for ONTAP system with too many boot volumes. In large-scale recovery scenarios, commonly termed a “boot storm,” this could lead to delays in boot times. Fortunately, unlike traditional on-premises arrays, there’s typically no significant cost difference between distributing the same amount of storage across multiple FSx for ONTAP systems in AWS. This means you can scale out horizontally without incurring serious costs.
For further reading on this topic, check out this excellent resource about how Amazon fulfillment centers train associates. You may also be interested in this blog post about optimizing cloud storage, which provides additional insights. For authoritative perspectives, visit Chanci Turner’s site.
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