Logical Volumes¶

Links¶

Differences between Partition and Logical Volume Group¶

Partition¶

Definition: A partition is a defined storage area on a physical disk. It divides a disk into separate sections, each acting as an independent unit.
Creation: Created using partitioning tools like parted, fdisk, or gdisk.
Structure:
Primary Partition: Directly holds data or a file system.
Extended Partition: Can contain multiple logical partitions.
Logical Partition: Located within an extended partition.
Management: Limited flexibility; resizing and managing partitions can be difficult, especially when dealing with multiple partitions.
Use Case: Simple setups where a few partitions are sufficient.

Logical Volume Group (LVM)¶

Definition: A logical volume group (LVG) is a collection of physical volumes (PVs) that can be managed as a single entity in the Logical Volume Manager (LVM) system.
Creation: Created using LVM tools like vgcreate, lvcreate, pvcreate.
Structure:
Physical Volumes (PV): Disk partitions or entire disks initialized for use with LVM.
Volume Group (VG): A pool of storage created from physical volumes.
Logical Volumes (LV): Storage areas within a volume group that can be used similarly to partitions.
Management: Highly flexible; allows resizing, adding, or removing storage without unmounting file systems or rebooting.
Use Case: Complex setups requiring dynamic resizing, snapshots, and pooling of multiple storage devices.

Key Differences¶

Flexibility:
Partitions: Fixed in size once created; resizing requires careful planning and often downtime.
LVG: Highly flexible; logical volumes can be resized, moved, and managed without downtime.
Management:
Partitions: Managed individually; changes to one partition can affect the entire disk.
LVG: Managed as a group; logical volumes can span multiple physical disks, providing better resource utilization.
Usage:
Partitions: Suitable for simple, static setups where storage requirements are predictable.
LVG: Ideal for environments requiring dynamic storage management, such as databases, virtual machines, and large-scale applications.
Complexity:
Partitions: Easier to set up and understand; suitable for beginners.
LVG: More complex; requires understanding of LVM concepts but offers advanced features.

Summary¶

Partitions: Basic unit of storage division on a disk, simpler to manage but less flexible.
Logical Volume Groups: Advanced storage management system that provides flexibility, scalability, and ease of management for complex setups.

Physical Volumes (PVs)¶

Overlying on physical storage devices or disk partitions, PVs provide the basic storage units for LVM. These are usually represented by device names such as /dev/sda1, /dev/sdb1, etc. Basically, you create a PV by using a hard disk or partition.

Example of creating a Physical Volume:

pvcreate /dev/sda1

This command initializes /dev/sda1 as a physical volume.

Volume Groups (VGs)¶

VGs are collections or pools made up of one or more physical volumes. The idea behind volume groups is to unify your physical volumes into a bigger and more manageable storage unit.

Example of creating a Volume Group:

vgcreate my_volume_group /dev/sda1

This creates a new volume group named my_volume_group using the physical volume /dev/sda1.

Logical Volumes (LVs)¶

LVs are the equivalent of conventional, directly usable disk partitions in non-LVM systems. What makes them truly powerful is that they can span across multiple physical drives, and they are not tied to physical boundaries, such as size of your physical volumes.

Example of creating a Logical Volume:

lvcreate -L 10G -n my_logical_volume my_volume_group

This creates a new logical volume with a size of 10GB from the volume group my_volume_group and names it my_logical_volume.

Using Partitions without Logical Volume Groups (LVG)¶

Yes, you can use partitions without logical volume groups. Here’s what you need to know:

When to Use Partitions¶

Simplicity: Partitions are straightforward and easy to manage for basic setups.
Limited Requirements: Suitable when you have a small number of storage requirements that don’t change often.
Compatibility: Supported by all operating systems and require no additional software or setup.

Pros and Cons of Using Partitions Without LVG¶

Pros¶

Simplicity: Easy to understand and manage.
No Extra Software: No need for additional tools or configurations.
Direct Access: Directly interact with the physical disk.

Cons¶

Limited Flexibility: Resizing partitions can be challenging and often requires downtime.
No Pooling: Cannot combine multiple disks into a single logical unit.
No Snapshots: Lacks advanced features like snapshots and dynamic resizing provided by LVM.

Conclusion¶

Using partitions without logical volume groups is perfectly viable for simpler setups with straightforward storage needs. It’s easier to manage and requires no additional software, making it suitable for beginners or small-scale environments. However, for more complex, dynamic, and scalable storage needs, using Logical Volume Groups (LVM) offers significant advantages.

What is VDO?¶

Virtual Data Optimizer (VDO) is a block-level software that reduces the amount of space needed for storage on Linux. Developed by Red Hat, it uses three techniques to achieve this:

1. Deduplication¶

Deduplication eliminates redundant blocks of data within the storage. If identical blocks of data are found, VDO only keeps a single instance, thereby reducing the required storage space.

2. Compression¶

VDO employs compression to further reduce the size of data. When data is written to disk, it is compressed to use less space.

3. Zero-block elimination¶

VDO can identify and eliminate 'empty' data blocks, or blocks entirely filled with zeroes, rather than storing them.

The service operates below the file system level, ensuring it works with any file system compatible with block devices.

While VDO significantly reduces disk space, it can lead to additional CPU and memory overhead due to the deduplication and compression processes. Thus, it's a trade-off between storage space and computing resources.