Create a file to host the fs.  Can also use dd here instead of truncate.     $ truncate -s 128M bigfile     $ du -csh bigfile     $ stat bigfile

Create a fs on the file. There will be some warnings saying it is not a block device.     $ mke2fs -t ext4 bigfile     $ stat bigfile 

Find the first unused loop device, then create it.     $ losetup -f     $ sudo losetup /dev/loop0 bigfile

Finnally, we can mount the fs.     $ sudo mkdir /mnt/fsof     $ sudo mount -t ext4 /dev/loop0 /mnt/fsof     $ mount | grep loop0     /dev/loop0 on /mnt/fsof type ext4 (rw,relatime,seclabel,data=ordered)

Now, let us do some experiments on the fs on a file.     $ sudo dd iflag=fullblock if=/dev/random of=largefile count=4096 bs=4096     The performance is not so good, be patient please.          $ sudo fallocate -p -o 4096 -l 8192 largefile      Puch a hole, and we can find the blocks used is reduced using:      $ du -c largefile     Or     $ stat largefile

Be careful to the unit of the different blocks, it may be a sector(512b), a fs block(1024b or 4096b).

=== How to Check Filesystem Block Size on Linux? Example 1:

tune2fs -l /dev/sda1 | grep -i ‘block size’

Block size: 4096 Example 2:

dumpe2fs -h /dev/sda1 |grep “Block size:”

Block size: 4096 Example 3:

blockdev –getbsz /dev/sda1

4096 Example 4:

echo “abc” >test.txt

du -h test.txt

4.0K test