superuser.se :: 1096565 :: Sparse disk image demo

root@box51 [/tmp]# truncate -s 10G /tmp/super-user-1096565.img
root@box51 [/tmp]# du -h /tmp/super-user-1096565.img
1.0K    /tmp/super-user-1096565.img
root@box51 [/tmp]# du -h --apparent-size /tmp/super-user-1096565.img
10G     /tmp/super-user-1096565.img
root@box51 [/tmp]# losetup -f
/dev/loop12
root@box51 [/tmp]# losetup /dev/loop12 /tmp/super-user-1096565.img
root@box51 [/tmp]# mkfs.ext4 -m0 /dev/loop12
mke2fs 1.45.5 (07-Jan-2020)
Discarding device blocks: done
Creating filesystem with 2621440 4k blocks and 655360 inodes
Filesystem UUID: a42204f3-a3d5-45fb-8c73-24bbda4f141b
Superblock backups stored on blocks:
        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632

Allocating group tables: done
Writing inode tables: done
Creating journal (16384 blocks): done
Writing superblocks and filesystem accounting information: done

root@box51 [/tmp]# mount -v /dev/loop12 /media
mount: /dev/loop12 mounted on /media.
root@box51 [/tmp]# dd if=/dev/urandom of=/media/1MB.garbage bs=1M count=1 status=progress
1+0 records in
1+0 records out
1048576 bytes (1.0 MB, 1.0 MiB) copied, 0.00596462 s, 176 MB/s
root@box51 [/tmp]# umount -v /dev/loop12
umount: /media (/dev/loop12) unmounted
root@box51 [/tmp]# du -h /tmp/super-user-1096565.img
1.3M    /tmp/super-user-1096565.img
root@box51 [/tmp]# du -h --apparent-size /tmp/super-user-1096565.img
10G     /tmp/super-user-1096565.img
root@box51 [/tmp]# cp -v /tmp/super-user-1096565.img /dev/shm/super-user-1096565.img
'/tmp/super-user-1096565.img' -> '/dev/shm/super-user-1096565.img'
root@box51 [/tmp]# du -h /dev/shm/super-user-1096565.img
5.3M    /dev/shm/super-user-1096565.img
root@box51 [/tmp]# du -h --apparent-size /dev/shm/super-user-1096565.img
10G     /dev/shm/super-user-1096565.img
root@box51 [/tmp]# df -hT /dev/shm /tmp
Filesystem     Type   Size  Used Avail Use% Mounted on
tmpfs          tmpfs   48G  5.3M   48G   1% /dev/shm
rpool/ROOT/os  zfs    1.5T  6.4G  1.5T   1% /