This chapter describes the Core and Edge components as a virtual storage system. It includes the following sections:

SteelFusion is a converged infrastructure solution, encompassing all branch services such as server, storage, networking, and WAN optimization. It is a dual-ended system that comprises two logical components: SteelFusion Edge and SteelFusion Core.

SteelFusion Core is a physical or virtual appliance in the data center that mounts all LUNs that need to be made available to applications and servers at a remote location from the back-end storage array. SteelFusion Edge provides a virtualized environment that hosts the branch application servers. Core appliances communicate across the WAN with the Edge appliances at the branch.

SteelFusion delivers local user performance while enabling data centralization, instant recovery, and lower total operating costs. Unlike traditional converged infrastructures, SteelFusion enables stateless branch services. You can access applications that run locally in your branch while the primary data is centralized in your data center. Decoupling computation from its underlying storage allows your applications to run in a stateless mode, which reduces your branch footprint and centralizes management of your branch services.

With the SteelFusion product family, data center administrators can extend a data center storage array to a remote location, even over a low-bandwidth link. SteelFusion delivers business agility, enabling you to effectively deliver global storage infrastructure anywhere you need it.

SteelFusion provides the following functionality:

By consolidating all storage at the data center and creating diskless branches, SteelFusion eliminates data sprawl, costly data replication, and the risk of data loss at the branch office.

The SteelFusion product family is designed to simplify infrastructure in remote offices and branch offices and manage it centrally from a data center. The SteelFusion product family is typically deployed in conjunction with SteelHeads and includes the following components:

For a list of qualified software and storage systems, we strongly recommend that you read the SteelFusion Interoperability Matrix at https://splash.riverbed.com/docs/DOC-4204.

For information on compatibility between SteelHead software (RiOS), Edge, Core, and vSphere releases, see the Riverbed Knowledge Base article RiOS, SteelFusion Edge, SteelFusion Core and vSphere Release Matrix at https://supportkb.riverbed.com/support/index?page=content&id=S27472.

The branch office server connects to the Edge, which implements handlers for the iSCSI protocol. The Edge also connects to the blockstore, a persistent local cache of storage blocks.

SteelFusion initially populates the blockstore using the following methods:

For details on blockstore population, see Blockstore prefetch and prepopulation.

Figure: Generic SteelFusion deployment shows the various components in a basic SteelFusion deployment.

At the data center, Core integrates with existing storage systems, virtual infrastructure, and SteelHead deployments. Core connects dedicated LUNs with each Edge appliance at the branch office.

The branch office server connects to Edge, which implements handlers for the iSCSI protocol. The Edge also connects to the blockstore, a persistent local cache of storage blocks within the Edge itself.

The blockstore is the Edge authoritative persistent cache of storage blocks. The blockstore is local from a branch perspective and holds blocks from all the LUNs available through a specific Edge. The blockstore is authoritative because it includes the latest-written blocks before they are sent through the Core to a storage array at the data center. When a server at the branch office requests data blocks, those blocks are served locally from the blockstore if those blocks are currently present. If they are not present, the Edge retrieves them through the Core from the data center LUN. Similarly, newly written blocks are spooled to the local blockstore, acknowledged by the Edge to the branch office server, and then asynchronously propagated to the data center. Because each Edge implementation is linked to one or more dedicated LUNs at the data center, the blockstore is authoritative for both reads and writes and can tolerate WAN outages without affecting cache coherency.

Blocks are transferred between the Edge and the Core through an internal protocol. The Core then writes the updates to the data center LUNs through the iSCSI or Fibre Channel Protocol (FCP). SteelFusion is designed to be coupled with the SteelHead WAN optimization. You can further optimize traffic between the branch offices and the data center by implementing SteelHeads.

For more information about Fibre Channel, see SteelFusion and Fibre Channel.

The data cache in the blockstore is stored as is, and it is not deduplicated. Edge appliances include the SteelHead, and in the data center, the Cores are coupled with SteelHead products, which assist with data reduction and streamlining between the Edge and the Core.

You can encrypt the blockstore cache at rest using AES 128/192/256-bit encryption. This encryption eliminates the risk if your appliances are stolen. Similarly, because SteelFusion enables the removal of physical tape media and backup devices traditionally used for data protection from the remote offices, this encryption also eliminates risk of data theft. As a result, the blockstore eliminates the need for separate block storage facilities at the branch office and all the associated maintenance, tools, backup services, hardware, service resources, and so on.

For more information about blockstore encryption, see At-rest and in-flight data security.

One of the drawbacks of block storage protocols like iSCSI or Fibre Channel communicating across a wide area network (WAN) is that the subsequent requests for further data blocks may be non-sequential to the point that they seem random. This randomness is by design and a facet of the backend storage, but it makes rapid data delivery across a WAN using a block storage protocol difficult due to the high-latency adding a long turnaround time between request and response.

One way to mitigate this effect is for the sending side to be able to predict in some way what the subsequent requests will be so that data can be sent without waiting for the request. However, this is not possible with traditional storage protocols.

The SteelFusion architecture is appropriate for this type of approach because data on the Edge is held locally in the blockstore. Blockstore is the persistent local cache of storage blocks linked to one or more dedicated LUNs at the data center. As long as the data blocks that the Edge wants to read are already in blockstore, no request needs to be transmitted across the WAN through the Core to backend storage. Instead, the Edge responds to the read request serving data at local disk speed. Since the Edge blockstore benefits from a three-tier architecture of memory, solid-state disk (SSD), and hard disk drive (HDD), the read response is faster than could be achieved by storage in traditional branch servers. But if the required data is not in blockstore (called a blockstore miss), the Edge requests the data from the backend storage by asking the Core. The Core understands specific blockstore formats and can send the requested data and also continue to proactively send across additional blocks of data to the blockstore that it predicts the Edge may need. If the prediction is successful, the Edge will then find the subsequent data it needs locally in the blockstore and therefore does not need to submit further requests to the Core.

Depending on the scenario, populating the Edge blockstore can be performed by one or more of these methods:

Smart prepopulation (sometimes referred to as intelligent prepopulation) - A type of prepopulation where the Core proactively sends all used blocks in a volume with no regards to the working set blocks. Smart prepopulation is only required if your pinned LUN is VMFS or NTFS.

For more information about how to enable or configure the different types of prepopulation, see the SteelFusion Command-Line Interface Reference Manual.