[ Thanks to Mayank
for this link. ]
“In the first part of this article we took a cursory
look at Linux Extended File System. This article goes deeper and
looks at the core of the filesystem concepts like blocks and their
contents.We have two kinds of blocks: Physical and Logical. Physical
blocks are those that reside on the actual storage media, where the
data is kept and has a fixed size. Logical blocks , on the other
hand, are those whose size is specified once the filesystem is
created. Logical blocks are further divided into smaller logical
units called as fragments. A logical block consists of an integral
number of fragments. This logical block size need not be the same
as the physical block size. It is the job of the file system driver
to provide the mapping from the logical block size to the physical
block size. A single logical block is divided into an integral
number of physical blocks. Ext2 has a default logical file size of
4k.”