Understanding Linux Ext Filesystems, RAID, and LVM: A Practical Guide
This article explains the structure of Linux Ext2/3/4 file systems, the role of superblocks and block groups, compares hardware and software RAID, and introduces LVM for flexible storage management, highlighting both benefits and risks.
Currently, the dominant Linux file systems are the Ext family (Ext2/3/4). An Ext file system consists of a superblock, an inode table, and data blocks.
Because storing all inodes and blocks together would be inefficient, Ext formats divide the disk into multiple block groups, each containing its own inode table, data blocks, and a copy of the superblock, similar to how a military division is organized into brigades.
Superblock
The superblock records essential information about the entire file system; without it the file system cannot exist. It stores:
Total number of blocks and inodes.
Counts of used and free blocks/inodes.
Block and inode sizes (blocks: 1 KB, 2 KB, 4 KB; inodes: 128 bytes).
Mount time, last write time, last fsck time, and other timestamps.
A valid‑bit indicating whether the file system is currently mounted (0) or not (1).
RAID
RAID devices are classified as hardware RAID or software RAID.
Hardware RAID uses a dedicated RAID controller card provided by the server vendor. It offers high performance, does not consume CPU or memory resources, but is expensive and requires driver installation.
Software RAID is implemented by the operating system. It consumes CPU and I/O resources but is inexpensive and easy to set up, making it suitable when budget is tight but data safety is required.
In Linux, the mdadm utility provides software RAID, supporting common RAID levels. Hardware RAID devices appear as /dev/sdX, while software RAID devices appear as /dev/mdX.
LVM (Logical Volume Manager)
Traditional partitioning fixes partition sizes; changing them requires re‑partitioning and reformatting. LVM solves this by allowing flexible resizing of file system capacity.
LVM does not improve performance or data safety. If LVM fails, all data stored on it may be lost. LVM aggregates several physical partitions or disks into a volume group (VG), which can then be divided into logical volumes (LV) that are mounted like regular partitions.
Source: Architecture Engineer Technical Alliance
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