How To Install, Configure and Manage VDO In Linux

In this Lesson, you will learn how what VDO in Linux is, and how to install, configure and manage VDO.

UNDERSTANDING THE SUBJECT MATTER

What Is VDO In Linux

VDO (virtual data optimizer ) is a storage technology used to maximally optimize storage space by compressing and eliminating the duplication of data on a storage device.

VDO uses LZ4 for compression, increases data throughput and a VDO volume can be created from a storage device such as a block device, raid, etc.

A VDO volume is a logical volume and can be specified to be larger than the physical volume it will be created from.

If a VDO size is not specified, the VDO volume will automatically take the size of the block device which makes VDO performs better.

On the other hand, if the logical volume is larger than the block device, there will be a larger space for your data but lesser performance compared to the former. Using VDO depends on what you want to achieve in your environment.

To use VDO, the vdo service must be up and running. The kmod-vdo kernel module must also be loaded.

How To Verify If VDO Daemon Is Running

To verify if VDO is running, use the command,

[root@server1 ~]# systemctl status vdo

● vdo.service - VDO volume services
   Loaded: loaded (/usr/lib/systemd/system/vdo.service; enabled; vendor preset: enabled)
   Active: active (exited) since Mon 2020-11-23 17:19:19 WAT; 18min ago

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How To Install VDO In Linux

To install VDO, use the command,

[root@server1 ~]# yum install vdo kmod-vdo

Updating Subscription Management repositories.
Red Hat Enterprise Linux 8 for x86_64 - BaseOS (RPMs)                            0.0  B/s |   0  B     00:21

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How To Start VDO In Linux

To start VDO In Linux, use the command,

[root@server1 ~]# systemctl start vdo

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How To Enable VDO In Linux

To enable VDO In Linux, use the command,

[root@server1 ~]# systemctl enable vdo

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How To Create a VDO Volume In Linux

To create a VDO volume in Linux without specifying the logical volume size, use the command,

# vdo create --name=<vdo-name> --device=/dev/<block-device>

To create a VDO volume by specifying the logical volume size, use the command,

# vdo create --name=<vdo-name> --device=/dev/<block-dev> --vdoLogicalSize=400G

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How To Start a VDO Volume In Linux

# vdo start --name=<vdo-name>

# vdo start --all

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How To Stop a VDO Volume In Linux

# vdo stop --name=<vdo-name>

# vdo stop --all

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How To Monitor / View The Statistics Of a VDO Volume In Linux

To view the status of a VDO volume in Linux, use the command,

# vdo status --name=<vdo-name>

To view the statistics of a VDO volume in Linux, use the command,

# vdostats <vdo-name>

# vdostats --hu <vdo-name>

# vdostats --verbose <vdo-name>.

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How To Delete a VDO Volume In Linux

To delete or remove a VDO volume in Linux, take the following steps below:

a). unmount the VDO volume

# umount <vdo-volume>

b). delete the VDO volume.

vdo remove --name=<vdo-name>

ACTION TIME

Having understood the VDO concept, let’s create a VDO volume using an example.

Step By Step Process Of How To Create a VDO Volume In Linux

create a VDO volume with a logical size of 100G and with the name, (tekneed_vdo) from (/dev/sdc). The volume should be formatted with the xfs filesystem and mounted on (vdo_data) which must be persistent across reboot.

1. verify if VDO and the kmod-kvdo module are installed. if not, install them.

[root@server1 ~]# rpm -q vdo kmod-kvdo

vdo-6.2.1.134-11.el8.x86_64
kmod-kvdo-6.2.3.114-74.el8.x86_64

On my server, they are installed but if they aren’t on your server, install them by using the command,

[root@DRDEV1 ~]# yum install vdo kmod-kvdo

Updating Subscription Management repositories.
Last metadata expiration check: 1:00:31 ago on Tue 17 Nov 2020 08:23:29 AM GMT.
Package kmod-kvdo-6.2.1.138-57.el8.x86_64 is already installed.
Dependencies resolved.
........

2. Verify the status of vdo service. If it is not started, start and enable VDO

[root@DRDEV1 ~]# systemctl status vdo

● vdo.service - VDO volume services
   Loaded: loaded (/usr/lib/systemd/system/vdo.service; enabled; vendor preset: enabled)
   Active: active (exited) since Mon 2020-11-16 15:31:39 GMT; 17h ago

VDO is started and enabled on my server. If it is not on your server, start and enable VDO by using the command,

[root@server1 ~]# systemctl enable --now vdo

3. create a vdo volume.

On my system. i will be creating the VDO volume on the sdc device with the name, tekneed_vdo.

Let’s list the devices on the system.

[root@server1 ~]# lsblk

NAME          MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda             8:0    0   15G  0 disk
├─sda1          8:1    0    1G  0 part /boot
└─sda2          8:2    0   14G  0 part
  ├─rhel-root 253:0    0 12.5G  0 lvm  /
  └─rhel-swap 253:1    0  1.5G  0 lvm  [SWAP]
sdb             8:16   0    2G  0 disk
sdc             8:32   0   10G  0 disk
sr0            11:0    1  7.3G  0 rom

create a VDO volume with a logical size of 100G. Though the original size of the disk is 10GB. We already explained in the “UNDERSTANDING THE SUBJECT MATTER” section that you can specify a logical volume size or not.

[root@server1 ~]# vdo create --name=tekneed_vdo --device=/dev/sdc --vdoLogicalSize=100G

Creating VDO tekneed_vdo
vdo: ERROR - Kernel module kvdo not installed
vdo: ERROR - modprobe: FATAL: Module kvdo not found in directory /lib/modules/4.18.0-147.el8.x86_64

NOTE: if you get the error above, it is a common bug with VDO as of when this article is written.

There are two workarounds. Either of the two workarounds below will work.

a). Try loading the kvdo module.

[root@server1 ~]# modprobe kvdo

modprobe: FATAL: Module kvdo not found in directory /lib/modules/4.18.0-147.el8.x86_64

b). if loading the kvdo module doesn’t work, reboot your system.

[root@server1 ~]# reboot

Now, Create the VDO volume

[root@server1 ~]# vdo create --name=tekneed_vdo --device=/dev/sdc --vdoLogicalSize=100G

Creating VDO tekneed_vdo
Starting VDO tekneed_vdo
Starting compression on VDO tekneed_vdo
VDO instance 0 volume is ready at /dev/mapper/tekneed_vdo

4. verify the created VDO volume

[root@server1 ~]# vdo list

tekneed_vdo

5. verify the vdo status

[root@server1 ~]# vdo status --name=tekneed_vdo
VDO status:
  Date: '2020-11-20 21:28:03+01:00'
  Node: server1
Kernel module:
......................

6. verify if compression and deduplication are enabled.

[root@server1 ~]# vdo status --name=tekneed_vdo |grep -i deduplication

    Deduplication: enabled

[root@server1 ~]# vdo status --name=tekneed_vdo |grep -i compression

    Compression: enabled

OR

[root@server1 ~]# vdo status --name=tekneed_vdo |grep -E 'Compression|Deduplication'

    Compression: enabled
    Deduplication: enabled

7. Format the VDO volume with a filesystem, xfs

[root@server1 ~]# mkfs.xfs -K /dev/mapper/tekneed_vdo

meta-data=/dev/mapper/tekneed_vdo isize=512    agcount=4, agsize=6553600 blks
         =                       sectsz=4096  attr=2, projid32bit=1
         =                       crc=1        finobt=1, 
.............

8. Register the new device in the kernel.

[root@server1 ~]# udevadm settle

9. Create a mount point.

[root@server1 ~]# mkdir /vdo_data

10. Map the VDO device to the mount point.

[root@server1 ~]# mount /dev/mapper/tekneed_vdo /vdo_data/

11. Verify if it has been mounted.

[root@server1 ~]# df -h |grep vdo_data

/dev/mapper/tekneed_vdo  100G  746M  100G   1% /vdo_data

12. get the device UUID

[root@server1 ~]# lsblk --output=UUID /dev/mapper/tekneed_vdo

UUID
71c9fada-81f9-4d84-b157-7b2edbb0e191

OR

[root@server1 ~]# blkid -p /dev/mapper/tekneed_vdo

/dev/mapper/tekneed_vdo: UUID="71c9fada-81f9-4d84-b157-7b2edbb0e191" TYPE="xfs" USAGE="filesystem"

13. input the device UUID in the fstab file.

[root@server1 ~]# vim /etc/fstab

UUID=71c9fada-81f9-4d84-b157-7b2edbb0e191 /vdo_data xfs defaults,x-systemd.requires=vdo.service 0 0

14. do a “mount -a” to ensure that the filesystem is properly mounted.

[root@server1 ~]# mount -a

15. If you wish, you can restart your system.

Let’s do a test

I mentioned that VDO manages files or data that are the same by compression and deduplication.

In this test, we will copy files of the same data multiple times to tekneed_vdo volume. We will verify the initial saving percentage before copying and the saving percentage after copying.

Let’s begin.

1. Verify the initial space of the filesystem

[root@server1 ~]# vdostats --hu
Device                    Size      Used Available Use% Space saving%
/dev/mapper/tekneed_vdo     10.0G      4.0G      6.0G  40%           99%

You can see that the volume size is 10G, used space is 4G which VDO has already taken, available space is 6G, and “space saving” is 99%

2. copy file1 to the VDO device

[root@server1 ~]# cp -r file1 /vdo_data/file1

Verify the statistics again

[root@server1 ~]# vdostats --hu

Device                    Size      Used Available Use% Space saving%
/dev/mapper/tekneed_vdo     10.0G      4.2G      5.8G  41%           28%

You can see that the new savings is 28%

3. copy file1 to the VDO device again

[root@server1 ~]# cp -r file1 /vdo_data/file2

verify the statistics

[root@server1 ~]# vdostats --hu

Device                    Size      Used Available Use% Space saving%
/dev/mapper/tekneed_vdo     10.0G      4.2G      5.8G  41%           58%

You can see that the new savings has increased to 58% instead of decreasing further from 28%.

4. copy file1 to the VDO device again

[root@server1 ~]# cp -r file1 /vdo_data/file3

Verify again.

[root@server1 ~]# vdostats --hu

Device                    Size      Used Available Use% Space saving%
/dev/mapper/tekneed_vdo     10.0G      4.2G      5.8G  41%           78%

Did you notice that the used space has remained the same while the savings space kept increasing?

This simple test has ascertained the fact that VDO is one of the finest storage technology in Linux for space efficiency.

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