Part one of working with logical volumes will cover the basic’s involved in creating logical volumes.
TL;DR
For those of you who just want the order of the commands.
sudo pvcreate </path/to/device> sudo vgcreate <vgname> </path/to/device> sudo lvcreate -n <lvname> -L <size> <vgname> sudo mkfs.<filesystem> </path/to/lv>
What you need to follow this guide
- A free disk (I used an empty virtual machine disk)
- Any Linux distribution (In this example I’ll be using Fedora 26, but the commands are the same across the entire Linux spectrum)
- LVM packages (lvm2 – usually pre-installed)
What is LVM?
Logical Volume Management (LVM) offers a way to abstract a disk, multiple disks, or disk partitions into one logical volume. LVM filesystems can be rearranged, resized, moved, removed, created, and deleted on the fly. They offer incredible flexibility when setting up a new system or when rethinking the storage layout of an existing system.
Logical Volume Management filesystems are made up of 4 major parts
- The physical device (physical volume)
- This is the storage device or devices that will make up the volume group.
- The Volume Group
- The volume group is essentially a disk or a group of physical devices that have been separated into a group. The Volume Group is just a pool of disks. It can contain just one disk (or partition), or many disks.
- The volume group is a logical volume made up of physical volumes
- The Live Volume
- the live volume is some portion of the volume group that will be dedicated to a particular filesystem. One volume group can have many live volumes.
- The filesystem
- After you create a Live Volume you must format it into one of the many Linux filesystems. Most likely ext4 or xfs.
Here is what you should remember if you are new to LVM
- Physical Volumes (the raw storage), make up Logical Volume Groups.
- Volume Groups are a logical representation of physical devices.
- Volume Groups contain Live Volumes which are formatted as filesystems.
- Filesystems are responsible for storing your data.
Create a new Volume
Step one – identify your storage device
We can identify our storage devices using the fdisk command
sudo fdisk -l Disk /dev/sda: 30 GiB, 32212254720 bytes, 62914560 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disklabel type: gpt Disk identifier: 0E3D261B-275C-49D0-8C9A-427B5CEEAD4F Device Start End Sectors Size Type /dev/sda1 2048 411647 409600 200M EFI System /dev/sda2 411648 2508799 2097152 1G Linux filesystem /dev/sda3 2508800 62912511 60403712 28.8G Linux LVM Disk /dev/sdb: 10 GiB, 10737418240 bytes, 20971520 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disk /dev/mapper/fedora-root: 25.8 GiB, 27703377920 bytes, 54108160 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes Disk /dev/mapper/fedora-swap: 3 GiB, 3221225472 bytes, 6291456 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 4096 bytes I/O size (minimum/optimal): 4096 bytes / 4096 bytes
The device I want is shown as “Disk /dev/sdb 10GiBâ€
Step two – create the physical volume
Use the pvcreate command to create the new physical volume.
sudo pvcreate /dev/sdb Physical volume "/dev/sdb" successfully created.
Step three – create the volume group
The vgcreate command, creates a new volume group
sudo vgcreate vgtest /dev/sdb Volume group "vgtest" successfully created
Step four – create a live volume
sudo lvcreate -n testlv -L 2G vgtest Logical volume "testlv" created.
Maybe another one
sudo lvcreate -n omg_testlv -L 2G vgtest Logical volume "omg_testlv" created.
lvcreate takes several arguments. You must specify a name, a size, and the volume group to attach it to.
Step five – make the filesystems
I’m formatting my filesystems as xfs in this case.
$ sudo mkfs.xfs /dev/mapper/vgtest-testlv
meta-data=/dev/mapper/vgtest-testlv isize=512 agcount=4, agsize=131072 blks
= sectsz=4096 attr=2, projid32bit=1
= crc=1 finobt=1, sparse=0, rmapbt=0, reflink=0
data = bsize=4096 blocks=524288, 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=4096 sunit=1 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
$ sudo mkfs.xfs /dev/mapper/vgtest-omg_testlv
meta-data=/dev/mapper/vgtest-omg_testlv isize=512 agcount=4, agsize=131072 blks
= sectsz=4096 attr=2, projid32bit=1
= crc=1 finobt=1, sparse=0, rmapbt=0, reflink=0
data = bsize=4096 blocks=524288, 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=4096 sunit=1 blks, lazy-count=1
realtime =none extsz=4096 blocks=0, rtextents=0
Step 3 – add the new filesystems to your fstab
Make a couple directories as mount points.
sudo mkdir /testlv sudo mkdir /omgtestlv
Edit the /etc/fstab file and append the following.
/dev/mapper/vgtest-testlv /testlv xfs defaults 0 0 /dev/mapper/vgtest-omg_testlv /omgtestlv xfs defaults 0 0
Mount the filesystems
sudo mount -a
How do I know that this did something?
Check your filesystem with df
df -hT Filesystem Type Size Used Avail Use% Mounted on devtmpfs devtmpfs 938M 0 938M 0% /dev tmpfs tmpfs 950M 0 950M 0% /dev/shm tmpfs tmpfs 950M 2.4M 948M 1% /run tmpfs tmpfs 950M 0 950M 0% /sys/fs/cgroup /dev/mapper/fedora-root ext4 26G 5.6G 19G 24% / tmpfs tmpfs 950M 28K 950M 1% /tmp /dev/sda2 ext4 976M 109M 800M 12% /boot /dev/sda1 vfat 200M 9.5M 191M 5% /boot/efi tmpfs tmpfs 190M 24K 190M 1% /run/user/42 tmpfs tmpfs 190M 40K 190M 1% /run/user/1000 /dev/mapper/vgtest-testlv xfs 2.0G 35M 2.0G 2% /testlv /dev/mapper/vgtest-omg_testlv xfs 2.0G 35M 2.0G 2% /omgtestlv
Notice our new volumes in the output of df.
Verify the Logical Volume with lvdisplay
sudo lvdisplay --- Logical volume --- LV Path /dev/vgtest/testlv LV Name testlv VG Name vgtest LV UUID zw2JB7-gmmZ-4llC-FLf1-jJhE-B82R-Xz4Cxc LV Write Access read/write LV Creation host, time fedora01, 2017-11-01 21:24:33 -0400 LV Status available # open 1 LV Size 2.00 GiB Current LE 512 Segments 1 Allocation inherit Read ahead sectors auto - currently set to 256 Block device 253:2 --- Logical volume --- LV Path /dev/vgtest/omg_testlv LV Name omg_testlv VG Name vgtest LV UUID h6eLKT-Aq5u-UXem-dgtA-OIXs-z901-lNRhNp LV Write Access read/write LV Creation host, time fedora01, 2017-11-01 21:25:28 -0400 LV Status available # open 1 LV Size 2.00 GiB Current LE 512 Segments 1 Allocation inherit Read ahead sectors auto - currently set to 256 Block device 253:3
If you are going to be working with LVM on a regular basis you will want to familiarize yourself with the following commands:
vgdisplay, vgscan, pvdisplay, pvscan, lvdisplay, lvscan
Helpful Links:
Luke has an RHCSA for Red Hat Enterpirse Linux 7 and currently works as a Linux Systems Adminstrator in Ohio.
This post, re-published here with permission, was originally published on Luke’s site here.
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