borg init -e repokey /path/to/repo
borg create /path/to/repo::Day1 ~/public_html
borg create -v --stats /path/to/repo::Day2 ~/public_html

performance-critical code (chunking, compression, encryption) is implemented in C/Cython
local caching of files/chunks index data
quick detection of unmodified files

lz4 (super fast, low compression)
zstd (wide range from high speed and low compression to high compression and lower speed)
zlib (medium speed and compression)
lzma (low speed, high compression)