How to verify size of pigz (parallel gzip) archive contents?

Question

I created some pigz (parallel gzip) - home page - compressed archives of my SSD disk drives. (compiled version 2.8)

I called one of them 4TB-SATA-disk--Windows10--2024-Jan-21.img.gz which says the size of the drive and the OS installed on it. Alternatively, the size is of course smaller in TiB which may be comfortably shown by fdisk and tools like it (Disk /dev/sda: 3.64 TiB).

I knew from the past, that listing the compressed file cannot show me the real size of contents. It will show 2.2GB or similar nonsense, even in Archive Manager for GNOME. It likely has something to do with gzip structure limitations.

However I had some doubts about the real size of the contents, therefore my question states how may I verify it?

xz doesn't have such limitations, can also be parallelized and compressed disk images can be mounted without having to decompress (and have better compression ratio, though take more effort to compress) — Stéphane Chazelas, Jan 27 '24 at 15:36
@StéphaneChazelas xz has the lowest performance, I can't imagine compressing a 4TB drive with it, the other comment I will inspect, thanks — Vlastimil Burián, Jan 27 '24 at 16:31

score 0 · Accepted Answer · answered Jan 27 '24 at 14:57

When I thought about it, I realized that without uncompressing the archive, this likely will not be possible, so I came up with the following:

$ cat 4TB-SATA-disk--Windows10--2024-Jan-21.img.gz | unpigz -p8 | pv >/dev/null 
3.64TiB 1:56:53 [ 543MiB/s] [ 543MiB/s] [            <=>                       ]

While I still hope there is some other way, I post my solution for the record.

How to verify size of pigz (parallel gzip) archive contents?

1 Answers1