structure of the disk
Because of the old saying in linux that "everything is a file", so for a file. Read and write, open and close all need corresponding functions: open(), read(), write(), close(). Devices are also considered files by Linux: block device: block, access unit "block", disk
Character devices: char, access unit "character", keyboard
You can view all device files that come with the system under /dev. Device files have major and minor device numbers
brw-rw----. 1 root disk 8, 1 Mar 31 06:03 /dev/sda1 crw-rw-rw-. 1 root root 1, 5 Mar 31 06:03 /dev/zero
Common disk interfaces are: SATA: 6Gbps, SAS: 6Gbps, USB: 480MB/s
Starting from CentOS6, all interface types of hard disks are named sd[a..z][number], and virtual disks are named vb.
In CentOS6, the newly added hard disk will be named as the first hard disk (sda), and in CentOS7, it will be named as the last hard disk.
Common types of disks are: mechanical hard drives and solid state drives.
Compared with HDD, SSD has obvious advantages in shock resistance, drop resistance, transfer rate, power consumption, weight, and noise. The transfer rate performance of SSD is twice that of HDD.
Compared with SSD, HDD has absolute advantages in price, capacity and service life
hard drive storage terms
head : head, track : track, cylinder : cylinder, sector : sector (512bytes)
Magnetic head = disk surface = disk * 2, number of tracks = number of cylinders
Because the sector with a small track number is large, and the sector with a large track number is small, the current mechanical hard disk uses ZBR (Zoned Bit Recording)
Disk addressing methods are: CHS and LBA addressing
CHS
uses 24bit bit addressing
where the first 10 bits represent the cylinder, the middle 8 bits represent the head, and the last 6 bits represent the sector
’s maximum addressing space of 8GB
LBA (logical block addressing)
LBA uses 48 bits to address
the maximum addressing space of 128PB
partition of the disk
Partitioning
MBR : Master Boot Record (Master Boot Record) uses 32 bits to indicate the number of sectors, and the partition does not exceed2T. According to the sector partition,in the 512 bytes of the 0 track 0 sector ofthe disk, the MBR of the hard disk is stored, and the details are written in thefile system foundation.
[root@CentOS6 ~]#hexdump -C /dev/sda -n 512 00000000 eb 48 90 10 8e d0 bc 00 b0 b8 00 00 8e d8 8e c0 |.H..............| 00000010 fb be 00 7c bf 00 06 b9 00 02 f3 a4 ea 21 06 00 |...|.........!..| 00000020 00 be be 07 38 04 75 0b 83 c6 10 81 fe fe 07 75 |....8.u........u| 00000030 f3 eb 16 b4 02 b0 01 bb 00 7c b2 80 8a 74 03 02 |.........|...t..| 00000040 80 00 00 80 70 13 05 00 00 08 fa 90 90 f6 c2 80 |....p...........| 00000050 75 02 b2 80 ea 59 7c 00 00 31 c0 8e d8 8e d0 bc |u....Y|..1......| 00000060 00 20 fb a0 40 7c 3c ff 74 02 88 c2 52 f6 c2 80 |. ..@|<.t...R...| 00000070 74 54 b4 41 bb aa 55 cd 13 5a 52 72 49 81 fb 55 |tT.A..U..ZRrI..U| 00000080 aa 75 43 a0 41 7c 84 c0 75 05 83 e1 01 74 37 66 |.uC.A|..u....t7f| 00000090 8b 4c 10 be 05 7c c6 44 ff 01 66 8b 1e 44 7c c7 |.L...|.D..f..D|.| 000000a0 04 10 00 c7 44 02 01 00 66 89 5c 08 c7 44 06 00 |....D...f.\..D..| 000000b0 70 66 31 c0 89 44 04 66 89 44 0c b4 42 cd 13 72 |pf1..D.f.D..B..r| 000000c0 05 bb 00 70 eb 7d b4 08 cd 13 73 0a f6 c2 80 0f |...p.}....s.....| 000000d0 84 f0 00 e9 8d 00 be 05 7c c6 44 ff 00 66 31 c0 |........|.D..f1.| 000000e0 88 f0 40 66 89 44 04 31 d2 88 ca c1 e2 02 88 e8 |[email protected]........| 000000f0 88 f4 40 89 44 08 31 c0 88 d0 c0 e8 02 66 89 04 |[email protected]..| 00000100 66 a1 44 7c 66 31 d2 66 f7 34 88 54 0a 66 31 d2 |f.D|f1.f.4.T.f1.| 00000110 66 f7 74 04 88 54 0b 89 44 0c 3b 44 08 7d 3c 8a |f.t..T..D.;D.}<.| 00000120 54 0d c0 e2 06 8a 4c 0a fe c1 08 d1 8a 6c 0c 5a |T.....L......l.Z| 00000130 8a 74 0b bb 00 70 8e c3 31 db b8 01 02 cd 13 72 |.t...p..1......r| 00000140 2a 8c c3 8e 06 48 7c 60 1e b9 00 01 8e db 31 f6 |*....H|`......1.| 00000150 31 ff fc f3 a5 1f 61 ff 26 42 7c be 7f 7d e8 40 |1.....a.&B|..}.@| 00000160 00 eb 0e be 84 7d e8 38 00 eb 06 be 8e 7d e8 30 |.....}.8.....}.0| 00000170 00 be 93 7d e8 2a 00 eb fe 47 52 55 42 20 00 47 |...}.*...GRUB .G| 00000180 65 6f 6d 00 48 61 72 64 20 44 69 73 6b 00 52 65 |eom.Hard Disk.Re| 00000190 61 64 00 20 45 72 72 6f 72 00 bb 01 00 b4 0e cd |ad. Error.......| 000001a0 10 ac 3c 00 75 f4 c3 00 00 00 00 00 00 00 00 00 |..<.u...........| 000001b0 00 00 00 00 00 00 00 00 89 1d 0b 00 00 00 80 20 |............... | 000001c0 21 00 83 aa 28 82 00 08 00 00 00 00 20 00 00 aa |! ... (....... ... | 000001d0 29 82 83 fe ff ff 00 08 20 00 00 00 40 06 00 fe |)....... ...@...| 000001e0 ff ff 83 fe ff 00 08 60 06 00 00 60 00 00 fe | ........ `...` ... | 000001f0 ff ff 05 fe ff ff 00 08 c0 06 00 f8 bf 05 55 aa |..............U.| 00000200
GPT : GUID (Globals Unique Identifiers) partition tablesupports 128 partitions, uses 64 bits to represent the number of sectors, and supports a maximum partition of 8Z (512Byte/block) or 64Z (4096Byte/block). Use 128-bit UUID (Universally Unique Identifier) to indicate that the disk and partition GPT partition table is automatically backed up in two copies at the head and tail, and has a CRC check bit.
Disks using GPT partitions are divided into: EFI information area (GPT header), partition table, GPT partition, and backup area.
Manage partitions
The lsblk command lists information about all available block devices and displays their dependencies, but it does not list information about RAM disks.
Syntax : lsblk [options] [device]
[root@CentOS6 ~]# lsblk --fs NAME FSTYPE LABEL UUID MOUNTPOINT sr0 iso9660 CDROM /media/CDROM sth ├─sda1 ext4 056668aa-7ecd-4235-8351-c8fb02372e3b /boot ├─sda2 ext4 481fa90c-b9f1-459b-ba67-f4f4c8d7942b / ├─sda3 ext4 b98328eb-21c7-4114-b3d5-93cd4aec6bc8 /data ├─sda4 ├─sda5 swap 5a1eda5a-2e54-4d0c-b8ea-ef99b9ac3417 [SWAP] └─sda6 ext4 /home 6caa3a45-0781-49bf-a167-9bfac5fa7fb5
Options :
-a, --all Display all devices.-f, Display file system information.
-m Display permission information.
-l, --list Display in list format.
fdisk is used to create and maintain MBR partition table; gdisk is used to create and maintain GPT partition table. The configuration does not take effect immediately, it takes effect after saving.
Syntax : fdisk [-l] [disk]
When using fdisk to manage MBR partitions on CentOS6, you need to use the -c option.
[root@CentOS6 ~]#fdisk -l
Disk /dev/sda: 107.4 GB, 107374182400 bytes
255 heads, 63 sectors/track, 13054 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000b1d89
Device Boot Start End Blocks Id System
/dev/sda1 * 1 131 1048576 83 Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2 131 6658 52428800 83 Linux
/dev/sda3 6658 7050 3145728 83 Linux
/dev/sda4 7050 13055 48233472 5 Extended
/dev/sda5 7050 7311 2097152 82 Linux swap / Solaris
/dev/sda6 7311 7572 2098730+ 83 Linux
[root@CentOS6 ~]#fdisk /dev/sda
WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
switch off the mode (command 'c') and change display units to
sectors (command 'u').
Command (m for help):
Subcommand :
p partition list
t change partition type
n create new partition
d delete partition
v verify partition
u convert unit
w save and exit
q do not save and exit
The parted command is an advanced disk maintenance tool that can manage and maintain MBR and GPT partitioned disks. Entering "parted disk" directly will enter the interactive mode, and the operation result of the parted command willtake effect immediately.
Syntax : parted [disk] [command]
[root@CentOS6 ~]#parted /dev/sda rm 6 Warning: WARNING: the kernel failed to re-read the partition table on /dev/sda (Device or resource busy). As a result, it may not reflect all of your changes until after reboot. Information: You may need to update /etc/fstab.
Subcommand :
mklabel: create a new partition type (partition table)
mkfs: create a file system for the partition with the specified label
mkpart: create a partition
mkpartfs: create a partition with a file system
name: name the partition with the specified number
print: print the partition table, Or partition
quit: quit the program
rm: delete the partition with the specified number
Sync partitions
View the partitions recognized by the current kernel:
[root@CentOS6 ~]#cat /proc/partitions major minor #blocks name 8 0 104857600 sda 8 1 1048576 sda1 8 2 52428800 sda2 8 3 3145728 sda3 8 4 1 sda4 8 5 2097152 sda5
[root@CentOS6 ~]#lsblk NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT sr0 11:0 1 5.8G 0 rom /media/CDROM sda 8:0 0 100G 0 disk ├─sda1 8:1 0 1G 0 part /boot ├─sda2 8:2 0 50G 0 part / ├─sda3 8:3 0 3G 0 part /data ├─sda4 8:4 0 1K 0 part └─sda5 8:5 0 2G 0 part [SWAP]
[root @ CentOS6 ~] #ls / dev / sda * / dev / sda / dev / sda1 / dev / sda2 / dev / sda3 / dev / sda4 / dev / sda5View existing partitions on the current disk:
[root@CentOS6 ~]#fdisk -l Disk /dev/sda: 107.4 GB, 107374182400 bytes 255 heads, 63 sectors/track, 13054 cylinders Units = cylinders of 16065 * 512 = 8225280 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disk identifier: 0x000b1d89 Device Boot Start End Blocks Id System /dev/sda1 * 1 131 1048576 83 Linux Partition 1 does not end on cylinder boundary. /dev/sda2 131 6658 52428800 83 Linux /dev/sda3 6658 7050 3145728 83 Linux /dev/sda4 7050 13055 48233472 5 Extended /dev/sda5 7050 7311 2097152 82 Linux swap / Solaris /dev/sda6 7311 7572 2098730+ 83 Linux
Most of the reasons for the out-of-sync is that the hard disk has been used for a period of time.
CentOS 6 can use the partx command to synchronize the partition table in memory with the hard disk.
Syntax : partx option disk
[root@CentOS6 ~]#partx -a /dev/sda BLKPG: Device or resource busy error adding partition 1 BLKPG: Device or resource busy error adding partition 2 BLKPG: Device or resource busy error adding partition 3 BLKPG: Device or resource busy error adding partition 4 BLKPG: Device or resource busy error adding partition 5
Options :
-a: Extra partition
-d --nr NM: reduce partitions
CentOS 7 can be synced using the partprobe command.