In order to properly migrate data, the source filesystem or directory
*must be read-only*. Changes made to files source may or may not be
propagated based on timing, and changes to the directory structure can
result in unrecoverable errors on the ZFSSA.
Shadow migration supports migration only from NFS sources. NFSv4 shares
will yield the best results. NFSv2 and NFSv3 migration are possible, but
ACLs will be lost in the process and files that are too large for NFSv2
cannot be migrated using that protocol. Migration from SMB sources is not