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In this tutorial, you’ll learn how to configure disk compression using Virtual Data Optimizer (VDO) in Linux. Although storage has become increasingly abundant and affordable, effective storage management remains crucial. VDO optimizes storage use through three key techniques: zero-block filtering, deduplication, and compression. Below, we explain each concept and provide step-by-step instructions to configure VDO on your system.
VDO enhances storage performance by filtering out unnecessary data, eliminating redundant blocks, and compressing data in real time.

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Zero-Block Filtering

VDO begins by scanning the storage device for blocks filled only with zeros—data that does not contribute meaningfully to the stored information. This process is similar to draining water from pasta using a colander: the water (empty data) flows away while the pasta (useful data) is retained.
The image illustrates a "Virtual Data Optimizer (VDO)" process, highlighting "Zero-Block Filtering" with a visual representation of data blocks containing binary numbers.
The image illustrates a concept of "Zero-Block Filtering" in a "Virtual Data Optimizer (VDO)" with a visual metaphor of a fork and colander with noodles. It also mentions "Deduplication" and "Compression" as part of the process.

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Deduplication

Once zero blocks are filtered out, VDO moves on to deduplication. In this step, VDO checks if a block of data is already present elsewhere on the storage device. If a duplicate is found, instead of rewriting the data, VDO updates its metadata to reference the existing block. This method reduces redundant data storage and conserves disk space.
The image illustrates the Virtual Data Optimizer (VDO) process, highlighting zero-block filtering, deduplication, and compression with a visual representation of data blocks.

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Compression

The final step in the VDO process is data compression. As data blocks are written to disk, VDO compresses them and packs several compressed blocks into one physical block. This not only saves space but can also improve read performance by reducing the amount of data transferred.

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Installing and Enabling VDO

If VDO is not already installed, you can add it using YUM. Once installed, enable and start the VDO service with systemctl:

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Creating a VDO Device

To begin using VDO, you must have a storage device. In this example, we use an unpartitioned device /dev/vdb (5 GB in size) and create a VDO device with a logical size of 10 GB:
Explanation of the command options:
  • vdo create: Initiates the creation of a new VDO-managed device.
  • --name=vdo_storage: Assigns a name to the new VDO device.
  • --device=/dev/vdb: Specifies the physical storage device to use.
  • --vdoLogicalSize=10G: Sets the logical volume size that users will see (10 GB logical, despite a 5 GB physical size).
After creating the VDO device, check its status with:
Expected output:
Here, the “Size” column reflects the physical capacity while “Use%” indicates current usage. The “Space saving%” field displays N/A until data is written.

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Creating a Filesystem on the VDO Device

Next, create an XFS filesystem on the VDO device. The -K option prevents XFS from sending discard requests, which accelerates filesystem creation on an all-zero VDO device:
After filesystem creation and letting udev settle, check the VDO statistics again:
The updated output should reflect a significant space-saving percentage:

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Mounting the VDO Device

Before mounting the VDO device, create a mount point (e.g., /mnt/myvdo) and add an entry to /etc/fstab with the necessary options to ensure the VDO service is active before mounting:
Then, create the mount point and mount the filesystem:
Expected output:
Note that the physical size is 5 GB, but the logical size presented to users is 10 GB.

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Demonstrating Deduplication

To observe how VDO conserves disk space via deduplication, follow these steps:
  1. Create a 50 MB file with random data:
  2. Create 10 directories on the VDO mount point:
  3. Copy the file into each directory using a loop:
  4. Verify the mount point’s usage:
    Expected result:
  5. Check the VDO statistics:
    Expected output:
Next, copy another file with a different name into each directory:
Then verify the filesystem usage and VDO statistics again:
Expected output for filesystem usage:
And VDO stats might show:
As you add more identical copies, you will notice an increase in the space-saving percentage, demonstrating VDO’s effective deduplication—even when file names differ.

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VDO in RHEL 9 with LVM Integration

In RHEL 9, VDO is integrated with LVM, and the standalone Python-based VDO tools are no longer used. To create a new VDO volume using LVM, proceed with the following steps:
  1. Create a physical volume on /dev/vdb:
  2. Create a volume group named vdo_volume:
  3. Create a logical volume with VDO options:
  4. Create an XFS filesystem on the new VDO volume:
    Alternatively, to use an ext4 filesystem:
One clear advantage of the LVM-integrated approach in RHEL 9 is that it simplifies mounting by eliminating the complex options required in previous versions.

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Mounting the LVM-Based VDO Device

First, create a mount point:
Edit the /etc/fstab file with your preferred text editor (e.g., vi) and add the following line:
Then, mount the filesystem and verify the mount:
Expected output:
This confirms that the VDO volume has a logical size of 10 GB and is correctly mounted. For more details on LVM-based VDO options, refer to the manual pages:
This concludes our comprehensive guide on configuring disk compression with VDO. Enjoy the benefits of optimized storage and improved performance in your Linux environment!

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