| Logical Volume Manager | ||
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Logical Volume Manager, also known as LVM, manages storage devices for the Linux kernel. LVM enables the user to combine physical disks into a single partition. As such, a striped volume is created. In this article I will show the basic steps of creating virtual groups and logical volumes.
LVM is installable on Debian as lvm2.
apt-get install lvm2
In this example I will create a logical volume from two usb sticks.
$ fdisk -l /dev/sdb
Disk /dev/sdb: 7.5 GiB, 8053063680 bytes, 15728640 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
For every physical disk a physical volume must be created. Afterwards, we can join these physical volumes into a virtual group. Virtual groups, in turn, can hold one or multiple logical volumes.
$ pvcreate /dev/sdb
Physical volume "/dev/sdb" successfully created.
$ vgcreate vg_usbs /dev/sdb
Volume group "vg_usbs" successfully created
$ lvcreate -n lv_usbs --size 512m vg_usbs
Logical volume "lv_usbs" created.
An entry on the file system should be created by now. It's located in /dev/mapper/ and is, in our case, named vg_usbs-lv_usbs. The virtual group also exists, namely as /dev/vg_usbs. We can create another logical volume by executing the lvcreate command again.
$ ls -l /dev/mapper/
crw------- 1 root root 10, 236 Sep 2 16:52 control
lrwxrwxrwx 1 root root 7 Sep 2 16:52 vg_usbs-lv_usbs -> ../dm-0
$ ls -l /dev/vg_usbs
total 0
lrwxrwxrwx 1 root root 7 Sep 2 16:52 lv_usbs -> ../dm-0
$ lvcreate -n lv_usbs_1 --size 512m vg_usbs
$ ls /dev/dm-*
/dev/dm-0 /dev/dm-1
The entries in /dev/mapper are available to use as one would use disks normally. They're ready to get a file system and can be auto mounted in fstab, for which I reccomend to use blkid.
$ mkfs.ext4 /dev/mapper/vg_usbs-lv_usbs
mke2fs 1.43.4 (31-Jan-2017)
Creating filesystem with 131072 4k blocks and 32768 inodes
Filesystem UUID: f847738f-6c61-47b3-8f44-bedac88c7027
Superblock backups stored on blocks:
32768, 98304
Allocating group tables: done
Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done
$ mount /dev/mapper/vg_usbs-lv_usbs /mnt/usb/
$ ls -la /mnt/usb
lost+found
$ blkid /dev/mapper/vg_usbs-lv_usbs
/dev/mapper/vg_usbs-lv_usbs: UUID="f847738f-6c61-47b3-8f44-bedac88c7027" TYPE="ext4"
$ echo "UUID=f847738f-6c61-47b3-8f44-bedac88c7027 /mnt/usb ext4 errors=remount-ro 0 0" >> /etc/fstab
Every volume has a convenient command to display its content.
$ pvdisplay
--- Physical volume ---
PV Name /dev/sdb
VG Name vg_usbs
PV Size 7.50 GiB / not usable 4.00 MiB
Allocatable yes
PE Size 4.00 MiB
Total PE 1919
Free PE 1663
Allocated PE 256
PV UUID XexhMW-m0Wx-hhBC-A3wN-t10F-6xIc-XvGuZS
$ vgdisplay
--- Volume group ---
VG Name vg_usbs
System ID
Format lvm2
Metadata Areas 1
Metadata Sequence No 3
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 2
Open LV 0
Max PV 0
Cur PV 1
Act PV 1
VG Size 7.50 GiB
PE Size 4.00 MiB
Total PE 1919
Alloc PE / Size 256 / 1.00 GiB
Free PE / Size 1663 / 6.50 GiB
VG UUID d7psdI-BDoe-axqg-u2jX-qsdQ-rM3r-cYm9pd
$ lvdisplay
--- Logical volume ---
LV Path /dev/vg_usbs/lv_usbs
LV Name lv_usbs
VG Name vg_usbs
LV UUID gKI6t9-dcw2-fT50-4HfK-AQ9J-K1Is-g3OTB0
LV Write Access read/write
LV Creation host, time lvm-test, 2019-09-02 16:52:57 +0200
LV Status available
# open 0
LV Size 512.00 MiB
Current LE 128
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 254:0
--- Logical volume ---
LV Path /dev/vg_usbs/lv_usbs_1
LV Name lv_usbs_1
VG Name vg_usbs
LV UUID ntX80L-0WhW-jK2O-DipI-eBdd-Vktz-pJJLHd
LV Write Access read/write
LV Creation host, time lvm-test, 2019-09-02 16:58:47 +0200
LV Status available
# open 0
LV Size 512.00 MiB
Current LE 128
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 254:1
$ pvcreate /dev/mmcblk0
Physical volume "/dev/mmcblk0" successfully created.
$ vgextend vg_usbs /dev/mmcblk0
Volume group "vg_usbs" successfully extended
$ vgdisplay
--- Volume group ---
VG Name vg_usbs
System ID
Format lvm2
Metadata Areas 2
Metadata Sequence No 4
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 2
Open LV 1
Max PV 0
Cur PV 2
Act PV 2
VG Size 9.36 GiB
PE Size 4.00 MiB
Total PE 2396
Alloc PE / Size 256 / 1.00 GiB
Free PE / Size 2140 / 8.36 GiB
VG UUID d7psdI-BDoe-axqg-u2jX-qsdQ-rM3r-cYm9pd
$ lvextend -L +8G /dev/mapper/vg_usbs-lv_usbs
Size of logical volume vg_usbs/lv_usbs changed from 512.00 MiB (128 extents) to 8.50 GiB (2176 extents).
Logical volume vg_usbs/lv_usbs successfully resized.
$ fdisk -l /dev/mapper/vg_usbs-lv_usbs
Disk /dev/mapper/vg_usbs-lv_usbs: 8.5 GiB, 9126805504 bytes, 17825792 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Make sure you resize the filesystem to the new parition size. For EXT, use resize2fs. Use the approperiate tool
for the filesystem installed.
$ resize2fs /dev/mapper/vg_usbs-lv_usbs
resize2fs 1.43.4 (31-Jan-2017)
Resizing the filesystem on /dev/mapper/vg_usbs-lv_usbs to 2228224 (4k) blocks.
The filesystem on /dev/mapper/vg_usbs-lv_usbs is now 2228224 (4k) blocks long.
$ lvremove /dev/mapper/vg_usbs-lv_usbs*
Do you really want to remove active logical volume vg_usbs/lv_usbs? [y/n]: y
Logical volume "lv_usbs" successfully removed
Do you really want to remove active logical volume vg_usbs/lv_usbs_1? [y/n]: y
Logical volume "lv_usbs_1" successfully removed
$ vgremove vg_usbs
Volume group "vg_usbs" successfully removed
$ pvremove /dev/mmcblk0
Labels on physical volume "/dev/mmcblk0" successfully wiped.
$ pvremove /dev/sdb
Labels on physical volume "/dev/sdb" successfully wiped.
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