[ceph-users] why the export v2 image is so small compare with without it?

Hi all! I export the rbd image use the export v2 format and without it. The difference is the export v2 format image is more smaller than the image which do not use export v2 format. Can any body tell me why they are size is difference so huge? Thanks very much! root@controller:/mnt# rbd du images/35d69ca5-b4f7-499e-9719-331eee498bc4 NAME PROVISIONED USED 35d69ca5-b4f7-499e-9719-331eee498bc4@snap 40GiB 40GiB 35d69ca5-b4f7-499e-9719-331eee498bc4 40GiB 0B <TOTAL> 40GiB 40GiB root@controller:/mnt# rbd export --export-format 2 images/35d69ca5-b4f7-499e-9719-331eee498bc4 ./v2image Exporting image: 100% complete...done. root@controller:/mnt# du -sh ./v2image 9.8G ./v2image root@controller:/mnt# rbd export images/35d69ca5-b4f7-499e-9719-331eee498bc4 ./image Exporting image: 100% complete...done. root@controller:/mnt# du -sh ./image 40G ./image