This approach contemplates storing the checkpoint block-allocated list in the metadata file as a list of 8B offset/size pairs, and that's relatively large. (This isn't accidental: I'd debug the whole thing before I'd mess with anything like bitmaps that will make it harder to track what blocks we're shuffling around.)

Other alternatives are compressing each 8B value individually, block compressing the entire list, using a bitmap, range compression, your good idea goes here. We should decide if the current size is a problem and if we should compress the extent values and work to keep them in the metadata file, move them into another file, or something else: This ticket is only intended to consider what additional work tickets should be created.