Data is the most critical thing in the system, and the disk is the necessary hardware device to persist the data.

Disk Types

Hard Disk Drive (HDD)

Revolution Per Minute (RPM) I/O Per Second (IOPS) Description
5400-15000 50-210 The cost is low; it is possible to recover the data, suitable for database servers.

Solid State Drive (SSD)

Revolution Per Minute (RPM) I/O Per Second (IOPS) Description
None 5000 and above The cost is high; it is impossible to recover the data, suitable for application servers.

Disk Interface Types

Calculations between bits, Bytes, Mbps and MBps.

Abbr Calculation Description
b 8 bits = 1 Byte bit
B 1 Byte = 8 bits Byte
Mbps 8 Mbps = 1 MBps Megabits Per Second.
MBps 1 MBps = 8 Mbps MegaBytes Per Second.

Parallel Port

Name Speed (Mbps) Speed (MBps)
IDE 133 1064
SCSI 640 5120

Serial Port

Name Speed (Mbps) Speed (MBps)
SATA 768 6144
SAS 768 6144
USB 2.0 60 480
USB 3.0 640 5120

File Systems

Disk File System

Linux File System

Name Description
ext2 Second extended file system, designed for Linux systems.
ext3 A journaled form of ext2.
ext4 A follow up for ext3 and also a journaled filesystem with support for extents.
ReiserFS File system that uses journaling
XFS Used on SGI IRIX and Linux systems

Shared-disk File System

Name Description
GFS2 (Global File System) from Red Hat. Available for Linux under GPL. Symmetric (GDLM) or Asymmetric (GULM).
OCFS2 (Oracle Cluster File System) from Oracle Corporation. Available for Linux under GPL. Symmetric.

Distributed File System

Name Description
NFS Originally from Sun Microsystems is the standard in UNIX-based networks. NFS may use Kerberos authentication and a client cache.

Distributed Parallel Fault-tolerant File Systems

Name Description
Ceph A massively scalable object store.
GlusterFS A general purpose distributed file system for scalable storage.
MoosFS A fault tolerant, highly available and high performance scale-out network distributed file system.

Special-purpose File System

Pseudo and Virtual File Systems

Name Description
proc A pseudo-file system, used to access kernel information about processes.
tmpfs In-memory temporary file system (on Linux platforms)
specfs Special File System for device files.
sysfs A virtual file system in Unix-like operating systems holding information about buses, devices, firmware, filesystems, etc.

Disk and Partition Suffixes


Disks’ names usually start with sd followed by a, b, c, d, etc.

Name Meaning
sda First disk.
sdb Second disk.
sdc Third disk.
sdd Fourth disk.
sdN Nth disk.


Disks’ partitions usually start with sd{a|b|c|d} followed by 1, 2, 3, 4, etc.

Name Meaning
sda1 First disk’s first partition.
sda2 First disk’s second partition.
sda3 First disk’s third partition.
sda4 First disk’s fourth partition.
sdaN First disk’s Nth partition.

Format Types

Master Boot Record (MBR)

  • Used by the Basic Input Output System (BIOS) boot mode when booting the operating system.
  • Almost every PCs and Servers support BIOS.
  • Poor compatibility with other hardwares.
  • Supports Legacy programs.
  • Slower than UEFI.

Total MBR size is 512 bytes.

Description Size (Bytes) Purpose
Bootstrap code area 446 Run BootLoader and other necessary programs.
Primary partition tables 64 = 16 Bytes * 4 Create partition entries.
Boot signature 2 Check whether MBR is valid.

Global Unique Identifiers Partition Table (GPT)

  • Used by the Unified Extensible Firmware Interface (UEFI) boot mode when booting the operating system.
  • Later PCs and Servers support UEFI.
  • Good compatibility with other hardwares.
  • Doesn’t support Legacy programs.
  • Faster than BIOS.

Disk Modes

Cylinder Head Sector (CHS)

1000000 GB = 1 PB

Maximum Addressing Space (GB) Addressing (bits) Description
8 24 A legacy hard disk mode.

Logical Block Addressing (LBA)

1 PB = 1000000 GB

Maximum Addressing Space (PB) Addressing (bits) Description
128 48 A later hard disk mode.

Device Type


Show block devices:

ll /dev | grep '^b'


Show character devices:

ll /dev | grep '^c'

Device Numbers

Major Number

The fifth column of the device list:

ll /dev | grep '^c' | awk '{print $10, $5}'

Minor Number

The sixth column of the device list:

ll /dev | grep '^c' | awk '{print $10, $6}'


Create hard link:

ln awk_file awk_file_ln

Show files and linked numbers:

ll | awk '{print $9, $2}'
  • Will accumulate the linked number.
  • Can’t be applied to directory.
  • Can’t be created in different partitions.
  • The size of the link is the size of the original file.
  • Won’t accumulate the linked number.
  • Can be applied to directory.
  • Can be created in different partitions.
  • The size of the link is the length of the target path.

References Revolutions per minute, IOPS, Hard disk drive, List of file systems, Master boot record, GUID Partition Table, Device file, Block (data storage), 12.2 ln: Make links between files

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