Disks, filesystems, and inodes

You already know the tree from /. Underneath it sits the hardware: disks, partitions, filesystems. This chapter shows how an ordinary file becomes bytes on a specific device, and who keeps track of it.

Start with what the system sees as disks. lsblk draws block devices as a tree: the disk itself, its partitions, and their mount points.

$ lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
sda      8:0    0   40G  0 disk
├─sda1   8:1    0    1G  0 part /boot
└─sda2   8:2    0   39G  0 part /
sdb      8:16   0   20G  0 disk

sda is a whole disk, sda1 and sda2 are partitions on it, sdb is a second disk with no partitions and no mount point yet. You split a disk's size into partitio