Basic concepts of Linux disks (disks, partitions, MBR, GPT)

1. CHS (Cylinder-Head-Sector ):

Was an early method for giving addresses to each physical block of data on a hard disk drive.

1.1 Cylinder (cylindrical ):

A cylinder comprises (including,... ) [K? M'hpa? Z] the same track number on each platter,

Spanning (spanning) all such tracks into SS (traversing) each platter surface that is able to store data (without regard to whether or not the track is "bad ").

Thus, it is a three-dimen1_structure.

Any track comprising part of a specific cylinder can be written to and read from while the actuator assembly remains stationary,

And one way in which hard drive manufacturers have increased drive access speed has been by increasing the number of platters which can be read at the same time.

1.2 Head (Head ):

A device called a head reads and writes data in a hard drive by manipulating the magnetic (magnetic) [m? G'net? K] medium that composes the surface of an associated disk platter.

The most basic unit for reading a Head is a Head. Each Head has a size of 512 bytes.

1.3 Sector (Sector ):

A sector is the smallest storage unit that is addressable (addressable) by a hard drive, and all information stored by the hard drive is recorded in sectors.

Elephant cut cake

1.4 Track1.5 Block2. representation of disks in Linux

2.1 All Linux devices are abstracted as a file and saved in the/dev/directory.

2.2 disks are divided into (IDE, SATA, SAS, SCSI, and USB) by interface)

2.2.1 The IDE disk name is generally: hd [a-z], and [a-z] indicates the disk number;

2.2.2 SATA disks, SAS hard disks, SCSI hard disks, and USB disks are generally named sd [a-z], and [a-z] indicates the disk number;

For example, the first sata disk is/dev/sda.

The second sata disk is/dev/sdb.

List several common devices and their file names in Linux.

3. Partition Concept

3.1 divide a disk logic into several zones. Each zone is used as an independent disk for ease of use and management.

The names of different partitions are generally: device name + Partition Number

For example, the first partition of the first hard disk is sda1 and the second partition of the first hard disk is sda2.

The first partition of the second hard disk is sdb1, and the second partition of the second hard disk is sdb2.

* Partitioning is not a physical function of a hard disk, but a software function.

* Mainstream partition mechanisms are divided into MBR and GPT.

MBR is the most widely used partition mechanism in PC architecture computers.

4. MBR

4.1 MBR (Master Boot Record) is a traditional partitioning mechanism, which is applied to the vast majority of PC devices using BIOS Boot (Apple uses EFI ); many Server servers support BIOS and EFI boot.

4.2 features of MBR

4.2.1 advantages: MBR supports 32bit and 64bit systems;

4.2.2 disadvantages: 1) the number of partitions supported by MBR is limited; 2) MBR only supports hard disks not larger than 2 TB, A hard disk larger than 2 TB can only use 2 TB of space (but there are third-party solutions). The addressing space for MBR is only 32 bit long;

4.3 MBR structure: occupies the first 512 bytes of the hard disk

The first 446 bytes are Bootstrap Code Area (guiding different operating systems; different operating systems, guiding Code is different)

The next step is 4 16 bytes: corresponding to 4 Primary Partition Table information (Primary Partition Table)

The last two bytes: Boot Signature, always 55 and AA; 55 and AA are permanent signs, which indicate that the hard disk can be started.

5. MBR partitioning

MBR partitions are divided into primary partitions, extended partitions, and logical partitions.

5.1 primary partition: a hard disk can only create up to four primary partitions (because up to four primary partition table information can be created in the MBR partition table structure, that is, four 16 bytes of space, for example)

5.2 extended partition: an extended partition occupies the location of a primary partition.

5.3 logical partitions:

1) it is created based on extended partitions. First, there are extended partitions, and then the logical partitions are created based on the extended partitions. That is to say, to use logical partitions, you must first create extended partitions;

2) the space of the extended partition cannot be used directly. We must create a logical partition on the basis of the extended partition to be used;

3) Linux supports up to 63 IDE partitions and 15 SCSI partitions.

PEL: Primary Partition; Extended Partition; Logical Partition

6. GPT

GPT (GUID Partition Table): It is a newer partitioning mechanism that solves many shortcomings of MBR.

1) Support for disks larger than 2 TB: GPT has 64-bit addressing space, while MBR supports up to 32 bit addressing space addresses and up to 32 power 2, hard Disk Space is identified by address. Therefore, MBR only supports disks with a capacity of less than 2 TB.

2) backward compatible with MBR

3) However, the underlying hardware must support UEFI (Intel proposes a new generation boot system to replace BIOS), that is, the underlying hardware must use UEFI.

4) The 64-bit operating system is required.

5) both Mac and LInux support the GPT partition format.

6) Windows 7 64bit and Windows Server2008 64bit support GPT