dd can only backup your drive 1:1, so also the empty space is backupped, which, as you already see yourself, is pretty bogus, especially when the drive is pretty empty.
gzip like all other packers work on files, not drives or partitions. Depending on what's on that drive, you can use
tar or
rsync to create a copy of the filesystem, and then use such a packer to store them as a packed file. With BSD and I suppose also Linux partitions this will work. But if it's a Windows system partition/drive, this will not provide a bootable/running system, when you restore from such an archive.
As I said in another thread of yours, you could use
gparted to reduce the partitions sizes - shrink them down to have only very few empty space left, and then copy the whole partitions with it to collect them on another drive(s), or afterwards use dd to create image files of the partition, and save that file where you wanna keep it.
In my Windows days I used it a lot, and I have very good experiences with gparted. Was my #1 tool to resize, copy, move and backup my Windows partitions, since there is no other way to really backup a Windows' system drive/partition than to make a full clone of it.
gparted cannot handle ZFS or other BSD filesystems (look at the list, what it can provide on its homepage.)
And it's Linux only (comes by default with Ubuntu.) But it also comes as a live system. You simply download the image, write (just
dd) to and then boot and run from a small flash drive.
There are also others for that job, like clonezilla.
