Understanding Linux Ext Filesystem, RAID Types, and LVM Basics

Linux’s mainstream file systems are the Ext family (Ext2/3/4), which consist of a Super Block, an Inode table, and Data blocks. To avoid placing all inodes and blocks together, the filesystem is divided into multiple Block Groups, each containing its own inode, block, and superblock structures, similar to how a military division is organized into brigades.

The Super Block stores critical metadata for the entire filesystem, including:

Total number of blocks and inodes.

Counts of used and free blocks/inodes.

Block and inode sizes (e.g., block sizes of 1 KB, 2 KB, 4 KB; inode size of 128 bytes).

Mount time, last write time, and last fsck (filesystem check) time.

A valid‑bit flag indicating whether the filesystem is currently mounted (0) or not (1).

RAID can be provided either by dedicated hardware (hardware RAID) or by the operating system (software RAID). Hardware RAID relies on a separate RAID controller card, offering better performance without consuming CPU or memory, but it requires driver installation and is more expensive. Software RAID is implemented by the Linux mdadm utility, which creates RAID arrays using partitions or whole disks and appears as /dev/md0, /dev/md1, etc., while hardware RAID devices appear as /dev/sda, /dev/sdb, and so on.

LVM (Logical Volume Manager) adds flexibility by allowing dynamic resizing of storage volumes. Physical partitions or disks are combined into a Volume Group (VG); from this VG, Logical Volumes (LV) are created and can be resized as needed. LVM does not improve performance or data safety, and a failure of the LVM layer can result in permanent data loss.