NetApp SnapMirror Optimization

gzipSnapMirroring to disaster recovery site requires huge amount of data to be transferred over the WAN link. In some cases replication can significantly lag from the defined schedule. There are two ways to reduce the amount of traffic and speed up replication: deduplication and compression.

If you apply deduplication to the replicated volumes, you simply reduce the amount of data you need to be transferred. You can read how to enable deduplication in my previous post.

Compression is a less known feature of SnapMirror. What it does is compression of the data being transferred on the source and decompression on the destination. Data inside the volume is left intact.

To enable SnapMirror compression you first need to make sure, that all your connections in snapmirror.conf file have names, like:

connection_name=multi(src_system,dst_system)

Then use ‘compression=enable’ configuration option to enable it for particular SnapMirror:

connection_name:src_vol dst_system:dst_vol compression=enable 0 2 * *

To check the compression ration after the transfer has been finished run:

> snapmirror status -l

And look at ‘Compression Ratio’ line:

Source: fas1:src
Destination: fas2:dest
Status: Transferring
Progress: 24 KB
Compression Ratio: 3.5 : 1

The one drawback of compression is an increased CPU load. Monitor your CPU load and if it’s too high, use compression selectively.

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