Replicating Network Attached Storage (NAS) data to a Disaster Recovery (DR) site is quite easy when using big named NAS appliances such as NetApp or Isilon. Replication software is already built-in on these appliances – Snapmirror for NetApp and SyncIQ for Isilon. They just need to be licensed to work.

But how do you replicate terabytes, even petabytes of data, to a DR site when the Wide Area Network (WAN) bandwidth is a limiting factor? Replicating a petabyte of data may take weeks, if not months to complete even on a 622 Mbps WAN link, leaving the company’s DR plan vulnerable.

One way to accomplish this is to use a temporary swing array by (1) replicating data from the source array to the swing array locally, (2) shipping the swing frame to the DR site, (3) copying the data to the destination array, and finally (4) resyncing the source array with the destination array.

On NetaApp, this is accomplished by using the Snapmirror resync command. On Isilon, this is accomplished by turning on the option “target-compare-initial” in SynqIQ which compares the files between the source and destination arrays and sends only data that are different over the wire.

When this technique is used, huge company data sitting on NAS devices can be well protected right away on the DR site.