Really interesting - I didn't know you could concatenate gzip files, and indeed this would have worked better. Another thing I found out while researching this

Really interesting - I didn't know you could concatenate gzip files, and indeed this would have worked better. Another thing I found out while researching this earlier is the pigz -i / --independent option. It lets you create a seekable gzip file, albeit one which cannot easily be indexed except by brute force searching over the whole file for the block boundaries (so not as useful as seekable xz like we use here: https://libguestfs.org/nbdkit-xz-filter.1.html https://libguestfs.org/nbdkit-xz-filter.1.html)