In addition to its primary purpose of migrating data from remote sources, the same
mechanism can also be used to migrate data from local filesystem to another on the
ZFSSA. This can be used to change settings that otherwise can't be modified, such as
creating a compressed version of a filesystem, or changing the recordsize for a
filesystem after the fact. In this model, the old share (or subdirectory within a share)
is made read-only or moved aside, and a new share is created with the shadow property
set using the file protocol. Clients access this new share, and data
is written using the settings of the new share.