The Logical Volume Manager (LVM) is a user space tool set designed to provide a higher level management of disk storage on a linux system than the traditional approach of disks and partitions. This is achieved by creating a software abstraction of those physical devices.
This virtualization of the disks provides the following benefits:
The ability to create single logical volumes from multiple physical volumes or entire disks.
Management of large disk clusters by allowing hot swappable disks to be added and replaced without service downtime.
Allows for easy filesystem resizing without having to migrate data.
Create filesystem backups by taking snapshots of logical volumes.
While it is possible to create a logical volume using an un-partitioned disk we recommend that you use a partitioned one, if for no other reason than to inform software such as partitioning utilities that the disk is being used. This avoids the possibility of someone firing up a partitioning program, seeing an un-partitioned disk and attempting to use it for some other purpose.
The first thing to do is identify the disks available for use, to do this
use lvmdiskscan while on a compute instance; and while having Sudo
privileges.
root@lvm-test:~# lvmdiskscan
/dev/vda1 [ 11.00 GiB]
/dev/vdb [ 10.00 GiB]
/dev/vdc [ 10.00 GiB]
2 disks
1 partition
0 LVM physical volume whole disks
0 LVM physical volumes
This shows us that there are currently three disks available.
/dev/vda1, which is a partition on the disk /dev/vda
/dev/vdb and /dev/vdc, which are un-partitioned disks
For this example /dev/vdb will be used to create the logical volume.
There are several tools available for creating disk partitions, these include tools such as fdisk, parted and the GNU parted. This example will use gdisk and the steps are as follows:
load gdisk and select the disk to partition
type n to create a new partition
accept the defaults for partition number, first sector and last sector
type L to list the available partition types
type 8e00 to select Linux LVM
type p to view the partition information
type v to verify the integrity of the changes
type w to write the changes to disk
root@lvm-test:~# gdisk
GPT fdisk (gdisk) version 1.0.1
Type device filename, or press <Enter> to exit: /dev/vdb
Partition table scan:
MBR: not present
BSD: not present
APM: not present
GPT: not present
Creating new GPT entries.
Command (? for help): n
Partition number (1-128, default 1):
First sector (34-20971486, default = 2048) or {+-}size{KMGTP}:
Last sector (2048-20971486, default = 20971486) or {+-}size{KMGTP}:
Current type is 'Linux filesystem'
Hex code or GUID (L to show codes, Enter = 8300): L
0700 Microsoft basic data 0c01 Microsoft reserved 2700 Windows RE
3000 ONIE boot 3001 ONIE config 3900 Plan 9
4100 PowerPC PReP boot 4200 Windows LDM data 4201 Windows LDM metadata
4202 Windows Storage Spac 7501 IBM GPFS 7f00 ChromeOS kernel
7f01 ChromeOS root 7f02 ChromeOS reserved 8200 Linux swap
8300 Linux filesystem 8301 Linux reserved 8302 Linux /home
8303 Linux x86 root (/) 8304 Linux x86-64 root (/ 8305 Linux ARM64 root (/)
8306 Linux /srv 8307 Linux ARM32 root (/) 8400 Intel Rapid Start
8e00 Linux LVM a500 FreeBSD disklabel a501 FreeBSD boot
a502 FreeBSD swap a503 FreeBSD UFS a504 FreeBSD ZFS
a505 FreeBSD Vinum/RAID a580 Midnight BSD data a581 Midnight BSD boot
a582 Midnight BSD swap a583 Midnight BSD UFS a584 Midnight BSD ZFS
a585 Midnight BSD Vinum a600 OpenBSD disklabel a800 Apple UFS
a901 NetBSD swap a902 NetBSD FFS a903 NetBSD LFS
a904 NetBSD concatenated a905 NetBSD encrypted a906 NetBSD RAID
ab00 Recovery HD af00 Apple HFS/HFS+ af01 Apple RAID
af02 Apple RAID offline af03 Apple label af04 AppleTV recovery
af05 Apple Core Storage bc00 Acronis Secure Zone be00 Solaris boot
bf00 Solaris root bf01 Solaris /usr & Mac Z bf02 Solaris swap
bf03 Solaris backup bf04 Solaris /var bf05 Solaris /home
bf06 Solaris alternate se bf07 Solaris Reserved 1 bf08 Solaris Reserved 2
Press the <Enter> key to see more codes: 8e00
bf09 Solaris Reserved 3 bf0a Solaris Reserved 4 bf0b Solaris Reserved 5
c001 HP-UX data c002 HP-UX service ea00 Freedesktop $BOOT
eb00 Haiku BFS ed00 Sony system partitio ed01 Lenovo system partit
ef00 EFI System ef01 MBR partition scheme ef02 BIOS boot partition
f800 Ceph OSD f801 Ceph dm-crypt OSD f802 Ceph journal
f803 Ceph dm-crypt journa f804 Ceph disk in creatio f805 Ceph dm-crypt disk i
fb00 VMWare VMFS fb01 VMWare reserved fc00 VMWare kcore crash p
fd00 Linux RAID
Hex code or GUID (L to show codes, Enter = 8300): 8e00
Changed type of partition to 'Linux LVM'
Command (? for help): p
Disk /dev/vdb: 20971520 sectors, 10.0 GiB
Logical sector size: 512 bytes
Disk identifier (GUID): 53C22F21-ABBF-4478-B0F9-xxxxxxxxxxxx
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 20971486
Partitions will be aligned on 2048-sector boundaries
Total free space is 2014 sectors (1007.0 KiB)
Number Start (sector) End (sector) Size Code Name
1 2048 20971486 10.0 GiB 8E00 Linux LVM
Command (? for help): v
No problems found. 2014 free sectors (1007.0 KiB) available in 1
segments, the largest of which is 2014 (1007.0 KiB) in size.
Command (? for help): w
Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!
Do you want to proceed? (Y/N): y
OK; writing new GUID partition table (GPT) to /dev/vdb.
The operation has completed successfully.
Now checking the disk status should show that there is a new partition
root@lvm-test:~# lvmdiskscan
/dev/vda1 [ 11.00 GiB]
/dev/vdb1 [ 10.00 GiB]
/dev/vdc [ 10.00 GiB]
1 disk
2 partitions
0 LVM physical volume whole disks
0 LVM physical volumes
In order to use a storage device in a logical volume the disks must first be labelled as LVM physical volumes, this can be done this using pvcreate. While there is only /dev/vdb1 being added at this time it is possible to pass multiple devices at once.
Warning
Using the pvcreate command will wipe any data that already exists on your volume. Only use this command on an empty volume if you do not want to lose any existing data.
The pvs (or pvdisplay) command can then be used to confirm the status of the available physical volumes.
root@lvm-test:~# pvcreate /dev/vdb1
Physical volume "/dev/vdb1" successfully created
root@lvm-test:~# pvs
PV VG Fmt Attr PSize PFree
/dev/vdb1 lvm2 --- 10.00g 10.00g
The next step is to create a volume group. Once again, though only a single initial physical volume is being added it is possible to add multiple physical volumes at a time.
It is possible to use a single volume group per server to create a pool of LVM managed storage, and then allocate all logical volumes from that. Some possible scenarios where multiple volume groups are necessary are:
to achieve a sense of separation between operating system and user disks.
a need for disks with different extent sizes.
isolating data for performance reasons
Multiple volume groups also require separate physical groups as they cannot be shared across volume groups.
Using vgcreate, create the volume group. If no value is provided for the extents it will use the default of 4MiB. Volume group status can be confirmed using vgs (or vgdisplay).
root@lvm-test:~# vgcreate vg_data /dev/vdb1
Volume group "vg_data" successfully created
root@lvm-test:~# vgs
VG #PV #LV #SN Attr VSize VFree
vg_data 1 0 0 wz--n- 10.00g 10.00g
The final step is to create a new logical volume using the lvcreate command , we will call it ‘data’ and create it in the volume group ‘vg_data’.
In the output above it shows that the volume group has 10GB available. That
means that a logical volume could be created with any size up to that limit.
To create a 5GB partition for instance, specify the the size argument -l 5G
. For this example the new volume will use all of the available free space with
the following parameter -l 100%FREE.
root@lvm-test:~# lvcreate -l 100%FREE -n data vg_data
Logical volume "test" created.
root@lvm-test:~# lvdisplay
--- Logical volume ---
LV Path /dev/vg_data/data
LV Name test
VG Name vg_data
LV UUID LECR2H-OKRK-lPCG-voU1-HCWw-fdTZ-JXcAHc
LV Write Access read/write
LV Creation host, time lvm-test, 2018-02-07 00:21:10 +0000
LV Status available
# open 0
LV Size 10.00 GiB
Current LE 2559
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 252:0
Running lvmdiskscan now should show that the new LVM volume is present.
root@lvm-test:~# lvmdiskscan
/dev/vg_data/test [ 10.00 GiB]
/dev/vda1 [ 11.00 GiB]
/dev/vdb1 [ 10.00 GiB] LVM physical volume
/dev/vdc [ 10.00 GiB]
2 disks
1 partition
0 LVM physical volume whole disks
1 LVM physical volume
All that remains to be done now is to add a filesystem to the LVM and you will have a functional LVM. Once this is done you will need to follow the next section on how to mount your new volume.
root@lvm-test:~# mkfs.ext4 /dev/vg_data/data
mke2fs 1.42.13 (17-May-2015)
Creating filesystem with 2620416 4k blocks and 655360 inodes
Filesystem UUID: 7551809b-9164-4ae4-ace3-xxxxxxxxxxxx
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632
Allocating group tables: done
Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done
Once you have created a new LVM you will need to mount it before you are able to access the storage space it has. The following guide will cover how to mount your existing LVM onto your instance.
Note
If you are using an existing volume from a previous instance, you will need
to attach your volume to the new instance first. You can use
openstack server add volume <INSTANCE_NAME> <VOLUME_NAME> to do this.
First, we need to find the name of our LVM. The following code will show you which volumes are present:
root@lvm-test:~# lvmdiskscan
/dev/vg_data/test [ 10.00 GiB]
/dev/vda1 [ 11.00 GiB]
/dev/vdb1 [ 10.00 GiB] LVM physical volume
/dev/vdc [ 10.00 GiB]
2 disks
1 partition
0 LVM physical volume whole disks
1 LVM physical volume
From the previous section we know that /dev/vg_data/test is our LVM.
Once we have our volume, we then have to create a mount point and update our
fstab file with the information on our LVM and our newly created folder.
We update the fstab file so that whenever the server starts up, it mounts our
LVM automatically on our folder.
# We will create a folder called 'data' to serve as our mount point
root@lvm-test:~# mkdir /data
# We then update our fstab file to have our LVM mount on our '/data' folder.
root@lvm-test:~# cat /etc/fstab
LABEL=cloudimg-rootfs / ext4 defaults 0 0
/dev/vg_data/data /data ext4 defaults 0 0
# Once this is done, we use the following command to force all volumes listed in the fstab to mount:
root@lvm-test:~# mount -a
Finally, once we have updated our fstab and forced our LVM to mount, we can view the mount information of our volumes using the following:
# Output truncated for brevity
root@lvm-test:~# mount
...
/dev/mapper/vg_data-data on /data type ext4 (rw,relatime,data=ordered)
Once this is done, you should be able to access your LVM from your mount point.