Which command allows RSYNC to copy block device contents to another device?

The command that allows RSYNC to copy block device contents to another device is indeed RSYNC itself. RSYNC is a powerful file transfer tool that synchronizes files and directories between two locations over a network or locally. It is capable of handling file copying with great efficiency, particularly by only transferring changes and using delta transfers.

When copying block devices, RSYNC can be used in conjunction with the appropriate options to ensure that the metadata and content of the block devices are handled correctly. This may involve using options that specify how data is to be read from the source and written to the destination, as well as ensuring that special filesystems are recognized properly.

Other options mentioned, such as "rysnc," do not exist and are a typographical error. "Tar" is primarily used for archiving files into a single tarball rather than directly copying block devices, and "cp" is a traditional file copy command that doesn't provide the same capabilities or efficiency as RSYNC when it comes to incremental backups or synchronizing files across devices. Thus, RSYNC stands out as the most suitable command for copying block device contents to another device.