Which flag would you use in RSYNC to copy block device contents directly?

The flag used in RSYNC to copy block device contents directly is quite specifically designed to handle special files, such as block devices and character devices. Utilizing the -D flag allows RSYNC to preserve these attributes of special files during the transfer process. This means it will not only copy the files but also maintain their inode types and other relevant metadata, ensuring that the block device contents are correctly replicated at the destination.

The other flags do not serve this specific purpose. The -t flag typically preserves modification times, -g preserves group ownership, and the -j flag is not standard in this context. Therefore, the use of the -D flag is essential for users intending to transfer the content of block devices effectively and accurately with RSYNC.