tramp: Connection types
4.1 Types of connections to remote hosts
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“Inline method” and “external method” are the two basic types of access
methods. While they both use the same remote shell access programs,
such as ‘rsh’, ‘ssh’, or ‘telnet’, they differ in the file access
methods. Choosing the right method becomes important for editing files,
transferring large files, or operating on a large number of files.
The performance of the external methods is generally better than that
of the inline methods, at least for large files. This is caused by the
need to encode and decode the data when transferring inline.
The one exception to this rule are the ‘scp’-based access methods.
While these methods do see better performance when actually transferring
files, the overhead of the cryptographic negotiation at startup may
drown out the improvement in file transfer times.
External methods should be configured such a way that they don’t
require a password (with ‘ssh-agent’, or such alike). Modern ‘scp’
implementations offer options to reuse existing ‘ssh’ connections, which
will be enabled by default if available. If it isn’t possible, you
should consider 
Password handling, otherwise you will be
prompted for a password every copy action.
Info Catalog
tramp: Configuration
tramp: Inline methods