backup@amandaserver# amrestore -r /dev/nst0 hostname /foo/bar

This will uncompress your dumps, which are probably gzipped, and that
takes CPU and more disk bandwidth to write.  If they are compressed,
give '-c' to amrestore to leave them alone.

(IMHO amrestore should default to not changing compression, and have
options to force compression and force uncompression.)