InfoWorld review: Riverbed Steelhead rules the WAN

Riverbed's RiOS 6 continues the tradition of WAN performance gains while improving flexibility, ease, and application support

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The test mixes included CIFS with many small files (1,004 files but only 10.4MB in total size); CIFS with one large file (a 155MB ISO image); Excel four-step (an open-copy-save as-open process); a MAPI test that saves a 700K attachment from Exchange to the local drive; and an FTP test using the same 155MB ISO file as the single-file CIFS test. All tests were executed using Macro Scheduler for consistency and timing. In every case, I saw small but measureable improvements in data reduction and overall performance compared to previous RiOS releases. Like previous versions of RiOS, RiOS 6 delivered huge increases in performance compared to native, non-optimized WAN links. It literally cut transfer times from hours to minutes, and minutes to seconds, depending on the nature of the data and the link. (See Lab Notes for charts and figures.)

Deduplication and compression
One of the most important enhancements is to Riverbed's SDR (Scalable Data Referencing) engine. RiOS 6 now has three modes of operation for deduplicating and compressing data as it passes through the appliance. The default mode is the same deduplication engine found in previous versions and leans toward maximum data reduction using disk-based deduplication. The two new modes of operation, SDR-Adaptive and SDR-M, come into play when disk I/O becomes a bottleneck.

Both SDR-Adaptive and SDR-M make use of memory-based compression; the difference is that one is dynamic, and the other is a fixed setting. SDR-Adaptive will dynamically switch between disk-based deduplication and memory-based compression whenever it detects that the disk I/O is becoming a limiting factor. One scenario where SDR-Adaptive would be used is data replication over the WAN. Longer transactions with larger data sets can potentially cause disk latency to slow the data transfer. SDR-Adaptive switches between deduplication and compression to balance data reduction and the load on the storage system.

SDR-M turns off disk-based deduplication entirely, relying exclusively on memory-only data compression to eliminate any potential disk I/O penalty. You would use SDR-M whenever overall speed is more important than data reduction or in cases where disk latency is a constant issue -- such as when sending small chunks of data over a very fast WAN circuit.

While most networks will want to stay with the default setting, Riverbed is providing IT with a way to easily tailor the system to meet specific needs. I used the default SDR mode for all of my performance testing, and not once did I push the appliance's limits.

New to RiOS 6 is the ability to tune the Sequenced Data Reduction engine based on traffic type and overall performance needs. Options include traditional disk-based deduplication, memory-only optimization, and a dynamic mix of the two.
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