Scaling Namespaces and Optimizing Data Storage
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Effect of erasure coding on existing data

Erasure Coding (EC) is set on a per-directory basis; therefore, setting an EC policy on a new or existing directory does not affect existing data in the cluster. Unless Erasure Coding is explicitly set, the default 3x replication scheme continues to be used.

  • If you set an Erasure Coding policy on a non-empty directory, the existing files are NOT converted to use Erasure Coding. The default 3x replication will still be used for these existing files.

  • You can also move a file from a non-EC directory to an EC directory, or from an EC directory to a non-EC directory. This movement between EC and non-EC directories does NOT change the file's EC or replication strategy. The only way to convert an existing file from non-EC to EC is to copy the file into a directory with an EC policy. You can use distcp to copy files.