Disk management and file system

Tips ： When the article is finished , Directories can be generated automatically , How to generate it, please refer to the help document on the right

One 、 Disk base

1. Disk structure

The physical structure of the hard disk

Disc : A hard disk has multiple disks , Every disc 2 Noodles .
head : One head per side .

2. The data structure of the hard disk

A sector : The disc is divided into sectors , Each sector stores 512 Bytes of data , The smallest storage unit of a hard disk .

Magnetic track : Concentric circles with different radii on the same disk , It is a circular track drawn by the magnetic head on the surface of the disk .

cylinder : A cylindrical surface formed by the same radius of different disks , It consists of multiple tracks of the same radius circle .

Hard disk storage capacity = Number of heads × Magnetic track （ cylinder ) Count × Sectors per channel × Bytes per sector (512 byte )

You can use a cylinder / head / Sector to uniquely locate each area on the disk
Disk interface type
IDE、SATA、SCSI、SAS、 Fibre channel

3.MBR And disk partition representation

MBR In the first physical sector of the hard disk
MBR It contains the main boot program and partition table of the hard disk
The partition table has 4 Zone record area , The recording area of each zone accounts for 16 Bytes
Linux Put the hard disk 、 Devices such as partitions are represented as files

/dev/hda5

/dev/= Hardware directory where the device is located
hd=IDE equipment
a= Hard disk serial number a;b;c And so on in letters
5= The sequence number of the partition , In numbers

4. Disk partition structure

The number of primary partitions in the hard disk is only 4 individual
The number of primary and extended partitions is limited to 1~4
Extended partitions are subdivided into logical partitions
The ordinal number of the logical partition will always be from 5 Start

5. File system type

1.XFS file system
A partition where files and directory data are stored .

High performance log file system , Especially good at dealing with big files , Hold millions TB Storage space .
CentOS 7 The default file system used in the system .

2.swap, Exchange file system

by Linux The system establishes a switch partition

─ Generally set as physical memory 1.5~2 times

6.Linux Other file system types supported

EXT4 、FAT32、NTFS、LVM

Two 、 Check and confirm the new disk

1. fdisk command

fdisk -l [ Disk device ] or
fdisk [ Disk device ]
-n Means to add a new partition
-p Indicates print partition list
-q Exit without saving
-t Indicates that the partition is changed id( type )
-l Show all partition types ( Of id)
-w Save and exit

2. Create system files （ format )

mkfs -t xfs / dev/ sdb1 and mkfs.xfs / dev / sdb1

3./etc/fstab Meaning

stay /etc/fstab
In file , Each line records the mounting configuration information corresponding to a partition or device , This information consists of six fields from left to right （ Use spaces or tabs to separate ）, The meaning of each part is as follows .
/dev/sdb1 / xfs defaults 0 0
The first 1 Field : Device name or device volume label .
The first 2 Field : The location of the mount point directory of the file system . The first 3 Field : File system type , Such as xfs、swap etc. .
The first 4 Field : Mount parameters , namely mount command "-o" The parameters available after the option . for example ,defaults、rw、ro、noexec Each represents the default parameter 、 Can write 、 read-only 、 Disable executors .
The first 5 Field : Indicates whether the file system needs dump Backup (dump It's a backup tool ). General set to 1 It is necessary to , Set to o Will be dump Ignore .
The first 6 Field : This number determines the order in which disk checks are performed at system startup .0 It means no inspection ,1 It means priority inspection ,2 Next, check . The root partition should be set to 1, Other partitions are set to 2.
By means of /etc/ fstab
Add the corresponding mount configuration to the file , It can automatically mount the specified partition after startup .

4. expand df command

df The command is used to check the disk space usage of the file system , Permissions are all users .df Format [ options]

One T: Show file system type .
One h: Print out the file system size in an easy to understand format , for example 136KB、24MB、21GB.

Common combinations df -hT

5. Mount command and unmount

Mount file system

mount + Files to mount + Directory to mount to

Unmount the file system

unmount+ Device storage location
or
unmount+ Mount point location

Add lf Enforceability .

6.free command

[[email protected] /]# free
              total        used        free      shared  buff/cache   available
Mem:        3762948      448316     2901128       14736      413504     3075792
Swap:       8191996           0     8191996

Mem： Memory
swap： Swap partition

total: Total amount
usee： Already used
free： not used

free -h Display units
free -m With M Display in units

The cache is memory and cpu Storage area between , Used to store cpu Data read from memory multiple times , Read the same variable multiple times , The variable will be put into the cache , When called again, it fetches... Directly from the cache , Don't take... From memory , When the variable changes in memory , This can lead to memory invisibility problems ; The goal is to access memory faster .

A buffer is a storage area in memory .
Buffer is divided into kernel buffer and user buffer ; Different functions .
The kernel buffer is a network transport buffer , file io, Console input and other operations “ Transfer station ”, Is invisible memory , That is, users cannot directly use .

3、 ... and 、 experiment

Identify disks without restarting ：
echo "- - - "> /sys/class/scsi_host/host0/scan
echo "- - - "> /sys/class/scsi_host/host1/scan
echo "- - - "> /sys/class/scsi_host/host2/scan
Restart command ： reboot / init 6

[[email protected] ~]# fdisk -l

 disk  /dev/sda：64.4 GB, 64424509440  byte ,125829120  Sectors 
Units =  A sector  of 1 * 512 = 512 bytes
 Sector size ( Logic / Physics )：512  byte  / 512  byte 
I/O  size ( Minimum / The best )：512  byte  / 512  byte 
 Disk label type ：dos
 Disk identifier ：0x000a3ffd

    equipment  Boot      Start         End      Blocks   Id  System
/dev/sda1   *        2048      821247      409600   83  Linux
/dev/sda2          821248   109445119    54311936   83  Linux
/dev/sda3       109445120   125829119     8192000   82  Linux swap / Solaris

 disk  /dev/sdc：21.5 GB, 21474836480  byte ,41943040  Sectors 
Units =  A sector  of 1 * 512 = 512 bytes
 Sector size ( Logic / Physics )：512  byte  / 512  byte 
I/O  size ( Minimum / The best )：512  byte  / 512  byte 


 disk  /dev/sdb：21.5 GB, 21474836480  byte ,41943040  Sectors 
Units =  A sector  of 1 * 512 = 512 bytes
 Sector size ( Logic / Physics )：512  byte  / 512  byte 
I/O  size ( Minimum / The best )：512  byte  / 512  byte 

2. Plan the partition in the hard disk
Create, delete and change partitions in the hard disk using fdisk command , You can enter the interactive setting page
To the hard disk /dev/sdb Zoning as an example

[[email protected] ~]# fdisk /dev/sdb
 Welcome to use  fdisk (util-linux 2.23.2).

 Changes will stay in memory , Until you decide to write changes to disk .
 Think twice before using the write command .

Device does not contain a recognized partition table
 Use disk identifier  0x065664db  Create a new  DOS  Disk label .

3.p Instructions - List the partitions in the hard disk , View partition table

 command ( Input  m  get help )：p

 disk  /dev/sdb：21.5 GB, 21474836480  byte ,41943040  Sectors 
Units =  A sector  of 1 * 512 = 512 bytes
 Sector size ( Logic / Physics )：512  byte  / 512  byte 
I/O  size ( Minimum / The best )：512  byte  / 512  byte 
 Disk label type ：dos
 Disk identifier ：0x065664db

    equipment  Boot      Start         End      Blocks   Id  System

4.n Instructions - New partition , Create two primary partitions , Respectively 5g and 4g.

 command ( Input  m  get help )：n
Partition type:
   p   primary (0 primary, 0 extended, 4 free)
   e   extended
Select (default p): p
 Zone number  (1-4, Default  1)：
 start   A sector  (2048-41943039, The default is  2048)：
 The default value... Will be used  2048
Last  A sector , + A sector  or +size{
    K,M,G} (2048-41943039, The default is  41943039)：+^[[GG
G”. Hold the suffix ：“
 Support ：10^N: KB ( kilobytes ), MB ( Megabytes ), GB ( Gigabyte )
            2^N: K  ( About kilobytes ), M  ( About megabytes ), G  ( Yogi byte )
Last  A sector , + A sector  or +size{
    K,M,G} (2048-41943039, The default is  41943039)：+5GB
 Partition  1  Set to  Linux  type , The size is set to  4.7 GiB

 command ( Input  m  get help )：N
Partition type:
   p   primary (1 primary, 0 extended, 3 free)
   e   extended
Select (default p): p
 Zone number  (2-4, Default  2)：
 start   A sector  (9766912-41943039, The default is  9766912)：
 The default value... Will be used  9766912
Last  A sector , + A sector  or +size{
    K,M,G} (9766912-41943039, The default is  41943039)：+4GB
 Partition  2  Set to  Linux  type , The size is set to  3.7 GiB

5.n Instructions - Allocate all the remaining space to 3 A logical partition .

 command ( Input  m  get help )：n
Partition type:
   p   primary (2 primary, 0 extended, 2 free)
   e   extended
Select (default p): e
 Zone number  (3,4, Default  3)：
 start   A sector  (17580032-41943039, The default is  17580032)：
 The default value... Will be used  17580032
Last  A sector , + A sector  or +size{
    K,M,G} (17580032-41943039, The default is  41943039)：
 The default value... Will be used  41943039
 Partition  3  Set to  Extended  type , The size is set to  11.6 GiB

6. preservation

 command ( Input  m  get help )：w
The partition table has been altered!

Calling ioctl() to re-read partition table.
 Synchronizing disk .

7. Press p see

 command ( Input  m  get help )：p

 disk  /dev/sdb：21.5 GB, 21474836480  byte ,41943040  Sectors 
Units =  A sector  of 1 * 512 = 512 bytes
 Sector size ( Logic / Physics )：512  byte  / 512  byte 
I/O  size ( Minimum / The best )：512  byte  / 512  byte 
 Disk label type ：dos
 Disk identifier ：0x065664db

    equipment  Boot      Start         End      Blocks   Id  System
/dev/sdb1            2048     9766911     4882432   83  Linux
/dev/sdb2         9766912    17580031     3906560   83  Linux
/dev/sdb3        17580032    41943039    12181504    5  Extended

9. Create system files （ format ）

[[email protected] ~]# mkfs.xfs /dev/sdb
mkfs.xfs: /dev/sdb appears to contain a partition table (dos).
mkfs.xfs: Use the -f option to force overwrite.
[[email protected] ~]# mkfs.xfs /dev/sdb1
meta-data=/dev/sdb1              isize=512    agcount=4, agsize=305152 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=0, sparse=0
data     =                       bsize=4096   blocks=1220608, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
log      =internal log           bsize=4096   blocks=2560, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0
[[email protected] ~]# mkfs.xfs /dev/sdb2
meta-data=/dev/sdb2              isize=512    agcount=4, agsize=244160 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=0, sparse=0
data     =                       bsize=4096   blocks=976640, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
log      =internal log           bsize=4096   blocks=2560, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0
[[email protected] ~]# mkfs.xfs /dev/sdb3
mkfs.xfs: /dev/sdb3 appears to contain a partition table (dos).
mkfs.xfs: Use the -f option to force overwrite.

10. stay / Create a directory under directory ky21

[[email protected] ~]# mkdir /ky21

11. Permanently mount and view

[[email protected] /]# vim /etc/fstab

#
# /etc/fstab
# Created by anaconda on Tue Jun 21 00:03:15 2022
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
# UUID=f4fa0787-b442-43b8-b146-a8eb38d322be / xfs defaults 0 0
UUID=3f9e0dcc-ec8c-4b14-ad33-a34eedc3dcf8 /boot                   xfs     defaults        0 0
UUID=15a82917-6245-4027-8105-d89b1761f63b swap                    swap    defaults        0 0
/dev/sdb1                                 /ky21                    xfs    defaults        0 0
~                                                                                             
：wq                        Save and exit 

[[email protected] /]# mount -a           Mount with immediate effect       

[[email protected] /]# df -hT            see 
 file system         type        Capacity    Already used    You can use   Already used %  Mount point 
devtmpfs       devtmpfs  1.8G     0  1.8G    0% /dev
tmpfs          tmpfs     1.8G     0  1.8G    0% /dev/shm
tmpfs          tmpfs     1.8G   13M  1.8G    1% /run
tmpfs          tmpfs     1.8G     0  1.8G    0% /sys/fs/cgroup
/dev/sda2      xfs        52G  4.9G   47G   10% /
/dev/sda1      xfs       397M  213M  185M   54% /boot
tmpfs          tmpfs     368M     0  368M    0% /run/user/0
tmpfs          tmpfs     368M   16K  368M    1% /run/user/42
/dev/sdb1      xfs       4.7G   33M  4.7G    1% /ky21

[[email protected] /]# cat /etc/fstab          Or use this to check 

#
# /etc/fstab
# Created by anaconda on Tue Jun 21 00:03:15 2022
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
# UUID=f4fa0787-b442-43b8-b146-a8eb38d322be / xfs defaults 0 0
UUID=3f9e0dcc-ec8c-4b14-ad33-a34eedc3dcf8 /boot                   xfs     defaults        0 0
UUID=15a82917-6245-4027-8105-d89b1761f63b swap                    swap    defaults        0 0
/dev/sdb1                                 /ky21                    xfs    defaults        0 0