Whenever I wipe my PC, I use tar to make an archive of the whole system. This works, but having to decompress the whole archive to pull files out is very annoying. Is there another archive format that:
Preserves permissions (i.e., is Unix-y)
Supports strong compression (I use either zstd or xz depending on how long I can be bothered to wait)
Take a look at squashfs. This creates a compressed archive that can be mounted as a read-only filesystem to pull out individual files. It is very fast and likely already installed on your system.
My biggest data regret is rsync-ing or tar-ing up my systems to my fileserver as a backup mechanism. So much wasted space. Extremely difficult to find anything. Impossible to properly organize. These backup solutions improve the situation tremendously.
When I wipe my PC I always use Clonezilla. I have a separate /home partition and I usually copy /etc inside my user's home directory just before the cloning. I'd say you should give it a try.
fsarchiver is very nice. Not fast on pulling out files, but, I mean, it's infinitely faster than tar.
Only quit using it so much because zfs-send is the real big hammer.
Best part is it can regenerate partitions, or whatever, or you can restore a larger partition to a smaller one, all the cool permutations assuming the files actually fit. Can re-write users and permissions if you like, all the bells.
Support for basic file attributes (permissions, ownership, …)
Support for basic file-system attributes (label, uuid, block-size) for all linux file-systems
Support for multiple file-systems per archive
Support for extended file attributes (they are used by SELinux)
Support for all major Linux filesystems (extfs, xfs, btrfs, reiserfs, etc)
Support for FAT filesystems (in order to backup/restore EFI System Partitions)
Experimental support for cloning ntfs filesystems
Checksumming of everything which is written in the archive (headers, data blocks, whole files)
Ability to restore an archive which is corrupt (it will just skip the current file)
Multi-threaded lzo, gzip, bzip2, lzma/xz compression: if you have a dual-core / quad-core it will use all the power of your cpu
Lzma/xz compression (slow but very efficient algorithm) to make your archive smaller.
Support for splitting large archives into several files with a fixed maximum size
Encryption of the archive using a password. Based on blowfish from libgcrypt.
Oh, also you can always copy it over to an iso image and mount it, or a qcow or raw image of some kind for loop mount.