gzip, zstd or xz for archives I keep for years?
The tradeoff in one table:
| gzip | zstd | xz | |
|---|---|---|---|
| Compression | baseline | better | best |
| Speed | fast | fastest | slow |
| Decompress | fast | fastest | moderate |
| Ubiquity | everywhere | recent | common |
For long-term archives the deciding factor is not ratio but whether the format opens without installing anything in ten years, which still favours gzip for the outer layer.
A folder of photos compresses to 98% of its size.
JPEG and PNG are already compressed, so a second pass finds nothing and costs CPU. Compression helps text and helps structured binary; for media the win comes from deduplication instead, which is why backup tools chunk before compressing.
Is there a simpler version that gets most of the benefit?
Yes: do the first step, skip the automation, and revisit in a month. Most of the value is in the first step, and most of the cost is in making it repeatable before you know it is right.