From man df
:
Display values are in units of the first available SIZE from --block-size, and the DF_BLOCK_SIZE, BLOCK_SIZE and BLOCKSIZE environment variables. Otherwise, units default to 1024 bytes (or 512 if POSIXLY_CORRECT is set).
SIZE may be (or may be an integer optionally followed by) one of following: KB 1000, K 1024, MB 1000*1000, M 1024*1024, and so on for G, T, P, E, Z, Y.
The -k
switch is equal to --block-size=1K
, which means that the numbers are in multiples of 1024 bytes.
The ext3 and ext4 family of filesystems reserve a portion of the disk to keep it from becoming truly "100% full", for stability reasons, and so that the FS can store metadata in some of that space.
You can directly tweak how much of the space is reserved:
tune2fs -m 1 /dev/sdXX
replacing "1" with the percentage (0 to 100) of the disk to reserve, and "XX" with the device node and partition number of the device node, so in your case "XX" would be "b2".
Analogy: you have a full bus, and the only remaining seat is next to a very large person who occupies a seat and a half by himself. A person who is very insistent on getting a seat walks up and demands to sit there. Although most people would consider the second seat taken, this person is insistent. So the large person goes, "Whoa, OK!" and squishes in to allow them to sit. But as soon as 1 person gets off the bus and opens up another seat, even if the passenger next to the large person moves into a seat, most people still consider the bus to be 100% full, because nobody wants to sit next to the large person.
Source
You can also check this to see Reserved Blocks count…
dumpe2fs -h /dev/sdb2
To quote the very intelligent user who nailed the issue in the source above:
You will see "Available" go positive when
"Used" is reduced to below 0.95*136236548 blocks = 129424720 blocks
roughly.
(we have to adjust the "0.95" to the reserved % in your specific case, and the 136236548 blocks to the total block size of your device).
Best Answer
A (physical) file system is a disk or partition, formatted in a certain way, and containing data structures comprising directories and files.
Every physical file system has a root directory indicated as
/
in Linux.Now this structure maps to a logical view. A simple logical view maps one physical file system one-on-one to your logical file system. This is called 'mounting a file system'.
You can mount a physical file system (or part of it) to a different logical node, called a 'mount point'. This means, your physical file system root
/
can be mounted to your logical "directory"/my/logical/mount
.If your physical file system contains a file
rootfile
in its physical root directory, you may access exactly that file by its logical name/my/logical/mount/rootfile
.The physical location is still on the physical file system, your access through the "mount point" is just a logical link to access that data.
Mount are useful for organizing various file systems, for combining several disks/partitions into one logical structure, and to combine various disparate devices and views into the same structure, from disks, partitions, USB sticks, floppy drives, remote network drives and even terminals, all logically residing under your logical root
/
.