Files backed up by backshift are split into "chunks".

Those chunks are usually compressed with xz.

In this analysis, the compression didn't really help that much; this is probably because a lot of the data backed up was already compressed.

This is from my home backups on Feb 21, 2014.

Here's the table:

metric\compression?	compressed_sizes	uncompressed_sizes
minimum	3	1
maximum	4,194,306	4,194,304
count	3,895,853	3,895,853
sum	2,326,799,316,643	2,456,227,275,776
mean	597250.2855325907	630472.2677616429
median	569978	584498
mode	666	2,106
standard_deviation	651,080.773333	643,844.735223
median_absolute_deviation	557,144.000000	549,493.000000