Linux Disk Management and File Systems

1. Disk Structure

1. Physical Structure

Platters: The disk has multiple platters, each with 2 surfaces.

Read/Write Heads: Each surface has one read/write head (the number of heads corresponds to the number of platters).

2. Data Structure

Sectors: The platters are divided into multiple sectors, each storing 512 bytes of data (the minimum storage unit; if less than 512 bytes, it is counted as 512).

Tracks:

Cylinders:

3. Hard Disk Interface Types

4. Mechanical Hard Drives and Solid State Drives

2. Disk Partitioning

1. Reasons for Partitioning

• Optimize I/O performance

• Implement disk space quota limits and improve recovery speed

• Isolate system and applications

• Install multiple operating systems

• Use different file systems

2. Partitioning

Extended partitions cannot be used alone and must be divided into logical partitions.

3. Disk Partition Structure

There can only be 4 primary partitions on a hard disk.

The numbering of primary and extended partitions is limited to 1-4.

Extended partitions are further divided into logical partitions.

The numbering of logical partitions will always start from 5.

3. File Systems

XFS File System

• Partitions that store file and directory data

• A high-performance journaling file system

• The default file system used in CentOS 7 (supports data recovery)

SWAP, Swap File System

• Creates a swap partition for the Linux system

Other File System Types Supported by Linux

• FAT16, FAT32, NTFS

• EXT4, JFS

disk Command

• View or manage disk partitions

fdisk -l [disk device]

or

fdisk [disk device]

fdisk -l to view the overall status and partitioning of the hard disk

• Device: The device file name of the partition.

• Boot: Whether it is a boot partition. If so, it is marked with a “*”. Start: The starting position of the partition on the hard disk (cylinder number).

• End: The ending position of the partition on the hard disk (cylinder number).

• Blocks: The size of the partition, measured in blocks, with the default block size being 1024 bytes.

• Id: The system ID number corresponding to the partition. 83 indicates an XFS or EXT4 partition in Linux, while 8e indicates an LVM logical volume. LVM is a logical mechanism for managing disk partitions in the Linux operating system, which will be discussed in later chapters.

• System: The partition type. After a new hard disk device is recognized, new partitions can be created on that disk. In Linux, the processes of partitioning and formatting are relatively independent; the operations for formatting partitions will be explained in subsequent content.

Common Commands in Interactive Mode

• m, p, n, d, t, w, q

mkfs Command

• Make Filesystem, create a file system (formatting)

Boot partition: The partition that boots the system, marked with ” * “: boot partition.

echo “- – -” > /sys/class/scsi_host/host2/scan

Scan the SCSI bus without rebooting, directly scan the hard disk.

Change the type of a partition.

Delete a partition.

Steps: Partition —- Format —- Create new folder —– Mount to the new folder.

UUID Unique Identifier

4. Mounting and Unmounting File Systems

mount Command

• Mount file systems or ISO images to a specified directory

mount [ -t type] storage device mount point directory
mount -o loop iso image file mount point directory

umount Command

• Unmount an already mounted file system

umount storage device location
umount mount point directory

The above is for temporary mounting.

Setting Automatic Mounting of File Systems

In the /etc/fstab file, each line records the mounting configuration information for a corresponding partition or device. These details include six fields from left to right (separated by spaces or tabs), with the meanings of each part described below.

/dev/sdb1 / xfs defaults 00

• Field 1: Device name or device label.

• Field 2: The location of the file system’s mount point directory.

• Field 3: File system type, such as xfs, swap, etc.

• Field 4: Mount parameters, which can be used after the “-o” option in the mount command. For example, defaults, rw, ro, noexec represent default parameters, read-write, read-only, and disable execution, respectively.

• Field 5: Indicates whether the file system needs to be dumped for backup (dump is a backup tool). Generally set to 1 to indicate it is needed, set to 0 to be ignored by dump.

• Field 6: This number determines the order in which disk checks are performed at system startup. 0 means no check, 1 means priority check, and 2 means secondary check. The root partition should be set to 1, while other partitions should be set to 2.

By adding the corresponding mounting configuration in the /etc/fstab file, automatic mounting of specified partitions after boot can be achieved. For example, executing the following operation will add the configuration record for automatically mounting the partition /dev/sdb1.

Viewing Disk Usage

df Command

df [options] [file]

[root@localhost ~]# df -hT
Filesystem                       Type     Size    Used   Avail   Use%   Mounted on
/dev/mapper/VolGroup-Lv_root  ext4     6.7G   4.1G   2.3G   65%   /
/dev/sda1                      ext4     99M    11M    83M    12%   /boot
tmpfs                          tmpfs    252M   0      252M   0%    /dev/shm
/dev/sdb1                     ext4     19G    173M   18G    1%    /mailbox

Link: https://www.cnblogs.com/qfzr2508/p/15755874.html

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