Review: Riverbed Granite reins in remote servers

Granite Core and Edge appliances split the difference in branch office consolidation, running servers in the branch based on storage in the data center

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Bringing branch office servers and file shares back to the data center is generally easy to do, especially with the use of WAN optimization solutions. But sometimes -- for the sake of performance, practicality, or politics -- a server simply must remain in the branch. It was for these intransigent servers, and to satisfy the needs of both server-hugging branch offices and control-hungry IT, that Riverbed Granite was born.

By pairing appliances at the edge and at the core, Granite allows IT to "project" virtual machines and iSCSI storage volumes out to the branch office while keeping the actual assets in the data center. Through innovative technologies, Granite closes the gap between physical servers in the branch office and storage in the data center. As a result, VMware ESX and Microsoft Hyper-V servers running in the branch can launch virtual machines across the WAN, and the VMs can write back to storage located in the data center.

[ Also on InfoWorld: Review: Riverbed Steelhead closes the WAN gap | Use server virtualization to get highly reliable failover at a fraction of the usual cost. Find out how in InfoWorld's High Availability Virtualization Deep Dive PDF special report. ]

Granite is available as a stand-alone product or as a bundled component on a Steelhead EX appliance. When used in combination with Steelhead WAN acceleration, performance improves dramatically, especially on subsequent VM launches, to rival the speed of true local storage.

Store centrally, execute locally
Granite is a different kind of creature than Steelhead. Steelhead accelerates a wide range of TCP and UDP traffic over a WAN through application- and protocol-specific optimization engines. Steelhead also reduces bits over the WAN through data deduplication, and it compresses data to get more on the wire. Granite, on the other hand, is specifically designed to export iSCSI storage resources located in the data center across the WAN and present them as local storage.

There are two components to a Granite installation. The Granite Core appliance, which resides in the data center, is available in either physical or virtual versions. The Granite Edge appliance, which goes in the branch office, is available only as a physical appliance. It can be installed as a stand-alone device or as part of a Steelhead installation (Steelhead EX). Granite Core uses some digital trickery to export LUNs (that is, iSCSI disk volumes) from the data center out to Granite Edge. A server in the branch, such as VMware ESX or Microsoft Hyper-V, connects via iSCSI to these LUNs on Granite Edge, where they appear as local storage volumes.

Granite helps to overcome WAN latency in a few ways. First, writes are acknowledged and cached by the appliance at the branch, then forwarded over the WAN in the background. Reads are accelerated through prediction and prefetching, as well as by caching the most recently requested blocks at the edge and delivering them locally. Typically, five to 20 percent of the LUN will be cached at the branch (the Granite Edge will cache as much of the LUN as it has disk space available). However, you can ensure that the entire storage volume will be served locally by "pinning" the LUN to the Granite Edge (more on pinning below).