Linux learning my way (Section X)

=== === pick IX

LVM allows users to dynamically adjust resources on the hard disk. LVM technology between the hard disk partition and file system adds a logical layer that provides an abstraction of the volume group can be a combination of multiple disks and by rolling. Users do not have the underlying architecture and layout of the physical machine's hard disk can be achieved dynamically adjust the hard disk partition.

Logical Volume Manager technology structure:

PE basic units consisting of a hard disk: Physical Extent (PE default size 4.00MiB)

Physical volume PV: Physical Volume, may be a physical hard disk partition or RAID set.

Volume group VG: Volume Group

Logical Volume LV: Logical Volume

3.1, the deployment of logical volumes

LVM common deployment command:

Function / Command	Physical Volume Management	Volume Group Management	Logical Volume Management
scanning	pvscan	vgscan	lvscan
set up	pvcreate	vgcreate	lvcreate
display	pvdisplay	vgdisplay	lvdisplay
delete	pvremove	vgremove	lvremove
Spread	--	vgextend	lvextend
Narrow	--	vgreduce	lvreduce

(1) create a physical volume

[Root @ linuxprobe ~] # pvcreate / dev / sdb / dev / sdc // create a hard disk to / dev / sdb, / dev / sdc physical volume

Physical volume "/dev/sdb" successfully created

Physical volume "/dev/sdc" successfully created

[Root @ linuxprobe ~] # pvdisplay // check the created physical volume, volume group is empty

"/dev/sdc" is a new physical volume of "10.00 GiB"

--- NEW Physical volume ---

PV Name /dev/sdc

VG Name

PV Size 10.00 GiB

Allocatable NO

PE Size 0

Total PE 0

Free PE 0

Allocated PE 0

PV UUID 3eHCPs-SWDN-Q0xW-H35F-L8Hw-7oWT-FhrS21

"/dev/sdb" is a new physical volume of "10.00 GiB"

--- NEW Physical volume ---

PV Name /dev/sdb

VG Name

PV Size 10.00 GiB

Allocatable NO

PE Size 0

Total PE 0

Free PE 0

Allocated PE 0

PV UUID bYTCj6 DSP I1pI will VKw3 B5FW 5vetRr

(2) create a volume group

[Root @ linuxprobe ~] # vgcreate mlgvg / dev / sdb / dev / sdc // physical volumes / dev / sdb, / dev / sdc to create a volume group

Volume group "mlgvg" successfully created

[Root @ linuxprobe ~] # pvdisplay // check the created physical volumes, volume groups have been shown to

--- Physical volume ---

PV Name /dev/sdb

VG Name mlgvg

PV Size 10.00 GiB / not usable 4.00 MiB

Allocatable yes

PE Size 4.00 MiB

Total PE 2559

Free IN 2559

Allocated PE 0

PV UUID bYTCj6 DSP I1pI will VKw3 B5FW 5vetRr

--- Physical volume ---

PV Name /dev/sdc

VG Name mlgvg

PV Size 10.00 GiB / not usable 4.00 MiB

Allocatable yes

PE Size 4.00 MiB

Total PE 2559

Free IN 2559

Allocated PE 0

PV UUID 3eHCPs-SWDN-Q0xW-H35F-L8Hw-7oWT-FhrS21

[Root @ linuxprobe ~] # vgdisplay // Check creates a volume group

--- Volume group ---

VG Name mlgvg

System ID

format lvm2

Metadata Areas 2

Metadata Sequence No 1

VG Access read/write

VG Status resizable

MAX LV 0

Cur LV 0

Open LV 0

Max PV 0

Cur PV 2

Act PV 2

VG Size 19.99 GiB

PE Size 4.00 MiB

Total PE 5118

Alloc PE / Size 0 / 0

Free PE / Size 5118 / 19.99 GiB

VG UUID hxvsyg-U6OO-dK3f-WU4i-3Nrr-TYmP-Qy3yZR

(3) create a logical volume

[Root @ linuxprobe ~] # lvcreate -n mlglv -l 100 mlgvg // In -l parameter (the number of basic units PE) to create a logical volume mlglv, size 100 * 4M = 400M.

Logical volume "mlglv" created

[Root @ linuxprobe mlgvg] # lvcreate -n mlglv2 -l 200 mlgvg // In -l parameter (the number of basic units PE) to create a logical volume mlglv2, size 200 * 4M = 800M.

Logical volume "mlglv2" created

[Root @ linuxprobe ~] # lvdisplay // create logical view

--- Logical volume ---

LV Path /dev/mlgvg/mlglv

LV Name mlglv

VG Name mlgvg

LV UUID 52pQW5-Zhv0-WjoF-cMFO-kgjR-qlZR-ZDHkJ7

LV Write Access read/write

LV Creation host, time linuxprobe.com, 2020-03-06 19:36:15 +0800

LV Status available

# open 0

LV Size 400.00 MiB

Current LE 100

Segments 1

Allocation inherit

Read ahead sectors auto

- currently set to 8192

Block device 253:2

--- Logical volume ---

LV Path /dev/mlgvg/mlglv2

LV Name mlglv2

VG Name mlgvg

LV UUID 8rn2PC-bQcZ-MErf-ENBC-JC93-ekiF-AFxgbr

LV Write Access read/write

LV Creation host, time linuxprobe.com, 2020-03-06 19:41:37 +0800

LV Status available

# open 0

LV Size 800.00 MiB

Current LE 200

Segments 1

Allocation inherit

Read ahead sectors auto

- currently set to 8192

Block device 253:3

Note: xfs file system does not support LVM technology, so the LVM expansion and the need to use the ext4 file system to format the partition.

[Root @ linuxprobe ~] # mkfs.ext4 / dev / mlgvg / mlglv // file system is formatted

mke2fs 1.42.9 (28-Dec-2013)

Filesystem label=

OS type: Linux

Block size=1024 (log=0)

Fragment size=1024 (log=0)

Stride=0 blocks, Stripe width=0 blocks

102400 inodes, 409600 blocks

20480 blocks (5.00%) reserved for the super user

First data block=1

Maximum filesystem blocks=34078720

50 block groups

8192 blocks per group, 8192 fragments per group

2048 inodes per group

Superblock backups stored on blocks:

8193, 24577, 40961, 57345, 73729, 204801, 221185, 401409

Allocating group tables: done

Writing inode tables: done

Creating journal (8192 blocks): done

Writing superblocks and filesystem accounting information: done

[Root @ linuxprobe ~] # mkdir / mlglv1 // create a mount point, mount LVM logical volume created and see if mount successful.

[root@linuxprobe ~]# mount /dev/mlgvg/mlglv /mlglv1/

[root@linuxprobe ~]# df -h

Filesystem Size Used Avail Use% Mounted on

/dev/mapper/rhel-root 18G 3.2G 15G 19% /

devtmpfs 985M 0 985M 0% /dev

tmpfs 994M 80K 994M 1% /dev/shm

tmpfs 994M 8.9M 986M 1% /run

tmpfs 994M 0 994M 0% /sys/fs/cgroup

/dev/sr0 3.5G 3.5G 0 100% /mnt/cdrom

/dev/sda1 497M 119M 379M 24% /boot

/dev/mapper/mlgvg-mlglv 380M 2.3M 354M 1% /mlglv1

Note: If you need to turn on automatically mount a logical volume, you need to edit / etc / fstab configuration file, add the following content.

[root@linuxprobe ~]# vim /etc/fstab

# /etc/fstab

# Created by anaconda on Sun Feb 16 14:06:24 2020

# 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

/dev/mapper/rhel-root / xfs defaults 1 1

UUID=0026f461-b0a2-4d90-8304-7cb4d0575432 /boot xfs defaults 1 2

/dev/mapper/rhel-swap swap swap defaults 0 0

/dev/sr0 /mnt/cdrom iso9660 defaults 0 0

/dev/mlgvg/mlglv /mlglv ext4 defaults 0 0

/dev/mlgvg/mlglv2 /mlglv2 ext4 defaults 0 0

/dev/mlgvg/mlglv3 /mlglv3 ext4 defaults 0 0

Note: reboot After rebooting again, the system automatically mount the logical volume has been determined.

[root@linuxprobe ~]# df -h

Filesystem Size Used Avail Use% Mounted on

/dev/mapper/rhel-root 18G 3.2G 15G 19% /

devtmpfs 985M 0 985M 0% /dev

tmpfs 994M 80K 994M 1% /dev/shm

tmpfs 994M 8.9M 986M 1% /run

tmpfs 994M 0 994M 0% /sys/fs/cgroup

/dev/sr0 3.5G 3.5G 0 100% /mnt/cdrom

/dev/sda1 497M 119M 379M 24% /boot

/dev/mapper/mlgvg-mlglv2 772M 1.6M 714M 1% /mlglv2

/dev/mapper/mlgvg-mlglv 380M 2.3M 354M 1% /mlglv

/dev/mapper/mlgvg-mlglv3 477M 2.3M 445M 1% /mlglv3

(4) expansion of logical volumes

[Root @ linuxprobe ~] # lvextend -L 800M / dev / mlgvg / mlglv // logical volume / dev / mlgvg / mlglv expansion to 800M

Extending logical volume mlglv to 800.00 MiB

Logical volume mlglv successfully resized

[Root @ linuxprobe ~] # e2fsck -f / dev / mlgvg / mlglv // view the file system if there are problems.

e2fsck 1.42.9 (28-Dec-2013)

Pass 1: Checking inodes, blocks, and sizes

Pass 2: Checking directory structure

Pass 3: Checking directory connectivity

Pass 4: Checking reference counts

Pass 5: Checking group summary information

/dev/mlgvg/mlglv: 11/102400 files (0.0% non-contiguous), 23456/409600 blocks

[root@linuxprobe ~]# resize2fs /dev/mlgvg/mlglv

// reset the logical volume size, there is Red Hat's bug here, if you need to perform prompt "e2fsck -f / dev / mlgvg / mlglv" command again, you will need to do this several times to restart again or mount command or logic volume and then execute this command.

resize2fs 1.42.9 (28-Dec-2013)

Resizing the filesystem on /dev/mlgvg/mlglv to 819200 (1k) blocks.

The filesystem on /dev/mlgvg/mlglv is now 819200 blocks long.

[root@linuxprobe ~]# mount -a

[root@linuxprobe ~]# df -h

Filesystem Size Used Avail Use% Mounted on

/dev/mapper/rhel-root 18G 3.2G 15G 19% /

devtmpfs 985M 0 985M 0% /dev

tmpfs 994M 80K 994M 1% /dev/shm

tmpfs 994M 8.9M 986M 1% /run

tmpfs 994M 0 994M 0% /sys/fs/cgroup

/dev/sr0 3.5G 3.5G 0 100% /mnt/cdrom

/dev/sda1 497M 119M 379M 24% /boot

/dev/mapper/mlgvg-mlglv2 772M 1.6M 714M 1% /mlglv2

/dev/mapper/mlgvg-mlglv3 477M 2.3M 445M 1% /mlglv3

/dev/mapper/mlgvg-mlglv 767M 2.5M 721M 1% /mlglv

Note: Make sure that the operation of the logical volume / dev / mapper / mlgvg-mlglv has successfully expanded to 800M.

(5) the logical volume reduction

[root@linuxprobe mlglv]# cp /home/EPEL-linuxprobe.com.tar.bz2 ./

// copy data to a logical volume, narrow verify whether the logical volume will cause data loss.

[root@linuxprobe mlglv]# ll

total 125529

-rw-r - r--. 1 root root 128527996 Mar 6 19:53 EPEL-linuxprobe.com.tar.bz2

drwx------. 2 root root 12288 Mar 6 19:39 lost+found

[root@linuxprobe mlglv]# cd ..

Before [root @ linuxprobe /] # umount / mlglv // shrink logical volumes need to uninstall mount point.

[root@linuxprobe /]# e2fsck -f /dev/mlgvg/mlglv

// first check the file system if there are problems, to ensure that data is not lost if there is no problem can be the next step.

e2fsck 1.42.9 (28-Dec-2013)

Pass 1: Checking inodes, blocks, and sizes

Pass 2: Checking directory structure

Pass 3: Checking directory connectivity

Pass 4: Checking reference counts

Pass 5: Checking group summary information

/dev/mlgvg/mlglv: 12/204800 files (0.0% non-contiguous), 162135/819200 blocks

[Root @ linuxprobe /] # resize2fs / dev / mlgvg / mlglv 500M // followed by the re-set the logical volume size to 500M

resize2fs 1.42.9 (28-Dec-2013)

Resizing the filesystem on /dev/mlgvg/mlglv to 512000 (1k) blocks.

The filesystem on /dev/mlgvg/mlglv is now 512000 blocks long.

[Root @ linuxprobe /] # lvreduce -L 500M / dev / mlgvg / mlglv // Finally reduce the size of the logical volume 500M

WARNING: Reducing active logical volume to 500.00 MiB

THIS MAY DESTROY YOUR DATA (filesystem etc.)

Do you really want to reduce mlglv? [y/n]: y

Reducing logical volume mlglv to 500.00 MiB

Logical volume mlglv successfully resized

[Root @ linuxprobe /] # mount -a // mount, verify whether the logical volume reduced success.

[root@linuxprobe /]# df -h

Filesystem Size Used Avail Use% Mounted on

/dev/mapper/rhel-root 18G 3.2G 15G 19% /

devtmpfs 985M 0 985M 0% /dev

tmpfs 994M 80K 994M 1% /dev/shm

tmpfs 994M 8.9M 986M 1% /run

tmpfs 994M 0 994M 0% /sys/fs/cgroup

/dev/sr0 3.5G 3.5G 0 100% /mnt/cdrom

/dev/sda1 497M 119M 379M 24% /boot

/dev/mapper/mlgvg-mlglv2 772M 1.6M 714M 1% /mlglv2

/dev/mapper/mlgvg-mlglv3 477M 2.3M 445M 1% /mlglv3

/dev/mapper/mlgvg-mlglv 477M 125M 323M 28% /mlglv

[root@linuxprobe /]# cd /mlglv

[Root @ linuxprobe mlglv] # ll // verify that the data is lost.

total 125530

-rw-r -. r-- 1 root root 128527996 Mar 6 19:53 EPEL-linuxprobe.com.tar.bz2 // data is not lost

drwx------. 2 root root 12288 Mar 6 19:39 lost+found

Note: xfs file system can not be reduced, only increased.

Description: can be found by the following example, when creating a logical volume space is used up again using another physical volume to satisfy the logical volume space created according to a physical volume space.

[root@linuxprobe mlglv]# pvdisplay

--- Physical volume ---

PV Name /dev/sdb

VG Name mlgvg

PV Size 10.00 GiB / not usable 4.00 MiB

Allocatable yes

PE Size 4.00 MiB

Total PE 2559

Free IN 2109

Allocated PE 450

PV UUID bYTCj6 DSP I1pI will VKw3 B5FW 5vetRr

--- Physical volume ---

PV Name /dev/sdc

VG Name mlgvg

PV Size 10.00 GiB / not usable 4.00 MiB

Allocatable yes

PE Size 4.00 MiB

Total PE 2559

Free IN 2559

Allocated PE 0

PV UUID 3eHCPs-SWDN-Q0xW-H35F-L8Hw-7oWT-FhrS21

(6) The Logical Volume Snapshot

LVM snapshot volume function has two characteristics:

Snapshot volume must have a capacity equal to the capacity of the logical volume;
The snapshot volume for one time only, it will be immediately and automatically deleted once the restore operation.

[root@linuxprobe /]# lvcreate -L 500M -s -n mlglvsnap /dev/mlgvg/mlglv

// create a size of 500M, named mlglvsnap snapshot volume. -s create a snapshot volume.

Logical volume "mlglvsnap" created

[root@linuxprobe /]# lvdisplay

--- Logical volume ---

LV Path /dev/mlgvg/mlglvsnap

LV Name mlglvsnap

VG Name mlgvg

LV UUID 5C2nN7-klci-hfR2-I92v-Qw7y-sxIa-pFb566

LV Write Access read/write

LV Creation host, time linuxprobe.com, 2020-03-06 20:09:21 +0800

LV snapshot status active destination for mlglv

LV Status available

# open 0

LV Size 500.00 MiB

Current LE 125

COW-table size 500.00 MiB

COW-table LE 125

Allocated to snapshot 0.00%

Snapshot chunk size 4.00 KiB

Segments 1

Allocation inherit

Read ahead sectors auto

- currently set to 8192

Block device 253:5

[Root @ linuxprobe mlglv] # rm -rf warm-linuxprobe.com.tar.bz2

// delete a file, then restore the snapshot volume, verify whether the recovery was successful.

[root@linuxprobe mlglv]# ll

total 12

drwx------. 2 root root 12288 Mar 6 19:39 lost+found

[Root @ linuxprobe /] # umount / mlglv // restore files need to uninstall the mount point by the snapshot volume.

[root@linuxprobe /]# lvconvert --merge /dev/mlgvg/mlglvsnap

// restore the logical data protection through snapshot volume.

Merging of volume mlglvsnap started.

mlglv: Merged: 100.0%

Merge of snapshot into logical volume mlglv has finished.

Logical volume "mlglvsnap" successfully removed

[root@linuxprobe /]# mount -a

[root@linuxprobe /]# cd /mlglv

[root@linuxprobe mlglv]# ll

total 125530

-rw-r -. r-- 1 root root 128527996 Mar 6 19:53 EPEL-linuxprobe.com.tar.bz2 // verification confirmation data has been restored.

drwx------. 2 root root 12288 Mar 6 19:39 lost+found

[root@linuxprobe mlglv]#

Note: The snapshot volume, there is no complete recovery, snapshot creation of logical volumes can be restored only be used once.

(7) Removing a Logical Volume

A, uninstall the mount point

[root@linuxprobe /]# umount /mlglv

[root@linuxprobe /]# umount /mlglv2

[root@linuxprobe /]# umount /mlglv3

B, Vim edit delete / etc / fstab to automatically mount configuration.

C, delete the logical volume

[root@linuxprobe /]# lvremove /dev/mlgvg/mlglv

Do you really want to remove active logical volume mlglv? [y/n]: y

Logical volume "mlglv" successfully removed

[root@linuxprobe /]# lvremove /dev/mlgvg/mlglv2

Do you really want to remove active logical volume mlglv2? [y/n]: y

Logical volume "mlglv2" successfully removed

[root@linuxprobe /]# lvremove /dev/mlgvg/mlglv3

Do you really want to remove active logical volume mlglv3? [y/n]: y

Logical volume "mlglv3" successfully removed

D, delete the volume group

[root@linuxprobe /]# vgremove /dev/mlgvg

Volume group "mlgvg" successfully removed

E, remove the physical volume

[root@linuxprobe /]# pvremove /dev/sdb /dev/sdc

Labels on physical volume "/dev/sdb" successfully wiped

Labels on physical volume "/dev/sdc" successfully wiped

After the above operations are completed, then perform lvdisplay, vgdisplay, will not see the LVM information created before the time pvdisplay command to view information regarding LVM.

3.2, bug fixes

Note: If for an error to modify the configuration file and cause the system fails to start, you can modify the configuration mode by entering the following command-line operation to recover.

Example 1: The file system and mount point does not exist, but the / etc / fstab to mount configured to start automatically, will lead the host can not start.

reboot to restart the virtual machine operating system to enter the following interface, enter the password for the root user can modify the configuration file recovery.