Basic Concepts: Linux Disks

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Disk Interface



  • IDE (ATA): Bandwidth is 133 Mbps. IOPS is ~100. The interface can connect maximum 2 disks.

  • SCSI: IOPS is ~ 150. It can connects 8 or 16 disks

    • Ultrascsi320 - 320 MB/s

    • Ultrascsi640 - 640 MB/s



  • SATA: Bandwidth is 6 Gbps. IOPS is ~150. It can connects to 8 or 16 disks.

  • SAS: Bandwidth is 6 Gbps. IOPS is ~200. It can connects to 8 or 16 disks.

  • USB: Bandwidth is 480 MB/s. IOPS is vary.


Linux Disks


Disk (Device) Types


Block: Can be accessed randomly. Unit is "block".


Character: Can be accessed sequentially. Unit is "character".



Disk Files (FHS)


Files are under '/dev/'. Every disk (device) is file on Linux environment.


Device ID:


Major: Primary device ID. To identify device type for proper drivers.


Minor: Secondary device ID. It's the entree of specific device of same type of device.


Create new device:


# mknode



[root@centos] mknode /dev/usbtest b 100 231 
[root@centos] ll | grep test 
brw-r--r--. 1 root root 100, 231 Jul 1 11:02 usbtest

Disk Name


It's assigned by ICANN.


IDE: /dev/hd[a-z]


SCSI/SATA/USB/SAS: /dev/sa[a-z][0-9]


There are 3 identifications below. You also can identify disks by go to /dev/disk/by-*.




  • Device file name

  • Volume labels

  • UUIDs


Disk Partition


MBR: Master Boot Record. It stars on sector 0. Size is 512 bytes. It consist of 3 parts:




  • Bootloader and boot applications. Size is 446 bytes.

  • Partition tables. Maximum 4 tables. 16 bytes each. Size is 64 bytes.

  • MBR availability mark. '55AA' means "active". Size is 2 bytes.


The maximum 'Primary' partition tables are 4. If you need more than 4 partitions, you need to create 'Extend' partition as the last partition of the 4, then create 'Logical partitions' on top of 'Extend partition'. Labels of the 4 are start from 1 to 4. 'Logical partitions' always starts from 5.

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