Results of compressing the factory image* of a new 3TB drive with various methods:
| Method | Size | Time |
|---|---|---|
| gzip --fast | 16.7 GiB | Kept up with the drive |
| gzip --fast | gzip --fast | 501 MiB | Kept up with the drive |
| gzip --fast | gzip --fast | gzip --fast | 426 MiB | Kept up with the drive |
| gzip --fast | gzip --fast | gzip | 425 MiB | Kept up with the drive |
| gzip --fast | gzip | 444 MiB | Kept up with the drive |
| gzip --fast | gzip | gzip | 425 MiB | Kept up with the drive |
| gzip --fast | xz | 426 MiB | Kept up with the drive |
| xz --fast | 833 MiB | 3 days |
| xz --fast | gzip | 418 MiB | 3 days |
| xz --fast | xz --fast | 416 MiB | 3 days |
| xz --fast | xz | 408 MiB | 3 days |
| bzip2 --fast | 3.24 GiB | 38 days |
| bzip2 --fast | bzip2 --fast | 556 MiB | 38 days |
| bzip2 --fast | bzip2 | 445 MiB | 38 days |
| snappy | 133 GiB | Kept up with the drive |
| snappy | snappy | 6.80 GiB | Kept up with the drive |
| snappy | snappy | snappy | 856 MiB | Kept up with the drive |
| snappy | snappy | snappy | snappy | 583 MiB | Kept up with the drive |
| snappy | snappy | snappy | snappy | snappy | 580 MiB | Kept up with the drive |
To put it back when I'm done with the drive. If for some reason I sell the drive or return it for warranty service, I'm certainly not leaving my stuff on it, and it seems a teeny tiny bit rude to pass along a wiped (all \0s) drive, especially to a less tech-savvy person. Presumably someone finds value in the junk the manufacturer takes the trouble to pre-load the drive with.
So I stash it in case I don't run the drive into the ground myself. The cost of this is tiny: 0.015% in this case. Compare: The ext4 overhead is 0.12%. The default mke2fs -m reserved-blocks-percentage is 5%.