lvconvert

The lvconvert command is used in Linux Logical Volume Manager (LVM) to modify the properties of an existing logical volume (LV). It allows you to convert a logical volume to a different type or configuration. For example, you can convert a regular volume into a thinly provisioned volume, a mirrored volume, or even add or remove mirrors.

Syntax

lvconvert [options] <lvname>

Where:

• <lvname>: The name of the logical volume you want to modify (e.g., /dev/vgname/lvname).

Common Use Cases

Here are some common ways to use lvconvert:

1. Convert to a Mirrored Logical Volume

If you have a non-mirrored logical volume (LV) and want to convert it to a mirrored LV, you can use the following syntax. The --mirror option allows you to create a mirrored volume.

Example: Convert to a Mirrored Volume (RAID 1)

sudo lvconvert --mirror 1 /dev/vgname/lvname

• --mirror 1: This option specifies that one mirror copy should be created. You need at least two physical volumes in the volume group for mirroring.

• This command will add a mirror to the logical volume, giving you redundancy (RAID 1).

2. Convert to a Thin-Provisioned Logical Volume

You can convert a standard logical volume to a thin-provisioned volume (thin provisioning allows you to allocate space as needed, rather than reserving it all upfront).

Example: Convert to Thin Volume

sudo lvconvert --type thin /dev/vgname/lvname

• --type thin: Specifies that the logical volume should be converted to a thin-provisioned volume.

• This command will allow you to make better use of space by allocating space only when the data is actually written to the volume.

3. Convert Thin-Provisioned to Regular Volume

If you no longer need the thin provisioning and want to convert it back to a regular volume, you can use lvconvert with the --type option set to default.

Example: Convert Thin Volume to Regular Volume

sudo lvconvert --type default /dev/vgname/lvname

• --type default: Converts the thin-provisioned LV back to a standard LV, with space allocated upfront.

4. Convert to a Snapshot Volume

You can convert a regular logical volume into a snapshot logical volume, which is a read-only copy of the original logical volume that can be used for backups or testing purposes.

Example: Convert to Snapshot

sudo lvconvert --snapshot /dev/vgname/lvname

• --snapshot: Converts the logical volume into a snapshot, which is a point-in-time copy of the LV.

5. Add Mirrors to an Existing Logical Volume

If you have a mirrored logical volume and want to add more mirrors (i.e., create RAID 1+N), you can use lvconvert with the --addmirror option.

Example: Add a Mirror to an Existing LV

sudo lvconvert --addmirror 1 /dev/vgname/lvname

• --addmirror 1: Adds one additional mirror to the logical volume.

• You can add multiple mirrors (e.g., --addmirror 2 for two additional mirrors).

6. Remove a Mirror from a Logical Volume

If you want to reduce the number of mirrors in a mirrored LV, you can use the --removemirror option.

Example: Remove a Mirror

sudo lvconvert --removemirror /dev/vgname/lvname

• --removemirror: Removes one mirror copy of the logical volume. You cannot remove the last mirror if there's only one mirror left.

7. Convert to a Striped Logical Volume (RAID 0)

You can also convert a logical volume to a striped volume (RAID 0) for better performance.

Example: Convert to Striped Volume

sudo lvconvert --stripes 2 /dev/vgname/lvname

• --stripes 2: Specifies that the volume should be striped across two devices. You can increase this number for more stripes.

8. Convert to a Linear Volume (Remove Striping)

If you want to revert a striped logical volume to a regular linear volume, you can use the --type option:

Example: Convert to a Linear Volume

sudo lvconvert --type linear /dev/vgname/lvname

• --type linear: Converts a striped or mirrored volume back to a linear volume, removing any striping or mirroring configuration.

Example Outputs

1. Successfully converting to a mirrored volume:

   Conversion of /dev/vgname/lvname to a mirrored volume successful.

2. Successfully converting to a thin volume:

   Logical volume /dev/vgname/lvname converted to thin provisioning.

3. Adding a mirror to an existing volume:

   Logical volume /dev/vgname/lvname now has 2 mirrors.

Conclusion

The lvconvert command is a powerful tool in LVM that allows you to modify the characteristics of an existing logical volume, including converting it to a mirrored, striped, or thin-provisioned volume. It can also be used to add or remove mirrors from an existing logical volume, providing flexibility for RAID configurations and space management.

Key use cases include:

• Converting to or from mirrored (RAID 1) volumes.

• Converting to or from thin-provisioned volumes.

• Adding or removing mirrors and stripes for performance or redundancy purposes.