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试试Fedora 20里头的File System on File,布布扣,bubuko.com
试试Fedora 20里头的File System on File
原文：http://blog.csdn.net/zedware/article/details/21884243
