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
distcpto copy files.