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WAN Optimization and Network Appliance SnapMirror

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Organizations collect vast amounts of information, and storing it all is only the first challenge in comprehensive data management. NetApp’s SnapMirror application is a popular choice to automate the backup, duplication and recovery of data to ensure availability in the event of a disaster or user error. Quite often, that involves replicating large amounts of data across a wide area network.

WAN links, however, have higher latency and much less bandwidth than either a LAN or Fibre Channel network. Latency severely impacts the performance of protocols SnapMirror relies on for WAN communication, and the amount of data often dwarfs the bandwidth most organizations
can afford. Even using SnapMirror’s advanced differential backup techniques, the amount of data blocks touched on an array can still be significant, and much larger than can be moved across the WAN during the backup window. If differential backups take hours, and a mirror initialization takes days or longer, how can organizations effectively maintain backups? Or worse, how can they expect to restore them quickly in a real disaster?

The technologies in WAN Optimization
can significantly improve SnapMirror data transfers. WAN Optimization uses byte caching and compression, combined with TCP enhancements and bandwidth
management to achieve remarkable savings across the WAN.

Mirror initialization triggers a
massive amount of network traffic which is highly repetitive and very compressible. Differential Mirror updates also contain much repetition; although the data is new in each individual file block, the byte patterns between files are very redundant and respond well to compression and caching. Initialization, recovery, and update times are typically decreased by 90% with WAN Optimization deployments.

Blue Coat offers one solution which goes beyond just compression and protocol optimization, however, by providing bandwidth management to control access to network resources. Blue Coat's ProxySG appliances can prioritize traffic based on user, application, time of day and content, ensuring that SnapMirror gets the bandwidth it needs both during the backup
window, and in the event of an emergency restore.

Tests conducted in labs and within customers environments show that WAN Optimization significantly improves the performance of SnapMirror in real world scenarios. In one test, the time needed to finish a Mirror backup operation was reduced by 58% on the first (cold) pass, and subsequent backups by almost 90%. Bandwidth used to complete the backup or restore was also reduced by 85%. Such a dramatic improvement makes it possible for our customers to complete their backups within the nightly window again.

For a new mirror initialization, WAN Optimization reduced the overall time to clone by 41x; convenient for IT when creating mirrors, but that performance increase would be critical in the event of an actual restore due to data loss or disaster.
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