I also have experience with tar and zlib, which is best suited for backups of data of all sorts, but it's just not really convenient to backup whole partitions/disks, because it doesn't respect device files, as well as mountpoints or mounted partitions. But if you want to backup user data, like fits/raw image files, this is the go-to command. It can also work incrementally, so you don't need much space for more than one full backup on your backup space/medium.

When i was dealing with Unix in enterprise environments, i used a mix of dd images of base installs and incremental/differential tar archives, which got zipped on the fly. I also upgraded my Pi4 with a SDD, which sped up Stellarmate significantly. This, however, adds the burden to do some extra filecopy work in the process of freshly installing Stellarmate OS from official sd-crad image files, but on the upside, backups of the SSD (root partition) are lightning fast, only the boot-partition is still needed on the sd-card for the OS, to know to mount the root partition from the SSD.

Please post back your findings of using dd with the "sparse" option set, thanks

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