LVM

Migration Guide: Moving from LVM to ZFS

Migrating from Linux Logical Volume Manager (LVM) to ZFS offers a unified storage management solution that combines advanced file system features with integrated volume management. ZFS eliminates the need for separate tools like LVM for volume management, as it handles file systems, snapshots, and RAID functionality natively. This migration guide will cover the steps to transition from LVM to ZFS, ensuring data preservation and proper configuration of the new ZFS pool.

Why Migrate from LVM to ZFS?

Key reasons for migrating from LVM to ZFS include:

• Integrated Volume Management: ZFS combines both file system and volume management, simplifying administration and eliminating the need for separate tools like LVM and mkfs.
• Data Integrity: ZFS offers end-to-end checksumming, ensuring better protection against data corruption than LVM and traditional file systems like EXT4 or XFS.
• Snapshots: ZFS supports efficient, native snapshots without requiring external tools like LVM or third-party backup solutions.
• Advanced RAID: ZFS provides built-in RAID-Z (RAID-Z1, RAID-Z2, RAID-Z3) for redundancy, which is easier to configure and manage than LVM RAID setups.

Prerequisites

Before starting the migration, ensure the following:

• Backup Data: Back up the data on the LVM volumes. The migration process involves formatting disks, which will result in data loss if not properly backed up.
• Ensure Disk Space: Prepare additional disks for the new ZFS pool or ensure enough space to migrate data from the LVM volumes.
• Install ZFS Utilities: Install the necessary ZFS packages depending on the operating system.

For Ubuntu or Debian-based systems:

$ sudo apt install zfsutils-linux

For RHEL-based systems:

$ sudo yum install zfs

Step 1: Prepare the New ZFS Pool

1. Identify Available Disks: Use lsblk or fdisk -l to list available disks and identify the ones that will be used for the new ZFS pool.

$ lsblk

2. Create the ZFS Pool: Based on the disk configuration, create a ZFS pool. For example, to create a pool with a single disk:

$ sudo zpool create mypool /dev/sdb

For a mirrored pool configuration:

$ sudo zpool create mypool mirror /dev/sdb /dev/sdc

For RAID-Z1 (single parity):

$ sudo zpool create mypool raidz /dev/sdb /dev/sdc /dev/sdd

Replace mypool with the preferred pool name.

Step 2: Migrate Data from LVM to ZFS

1. Mount the LVM Logical Volume: First, ensure the LVM volume is mounted. If it's not already mounted, mount it using the LVM tools:

$ sudo mount /dev/mapper/vgname-lvname /mnt/lvm

2. Copy Data to the ZFS Pool: Use rsync to copy data from the LVM volume to the ZFS pool. This ensures file attributes, permissions, and symbolic links are preserved.

$ sudo rsync -aHAXv /mnt/lvm/ /mypool/

This command transfers all data from the LVM volume at /mnt/lvm to the ZFS pool at /mypool.

Step 3: Configure ZFS Features

1. Enable Compression: ZFS supports several compression algorithms, such as lz4 (default). Enable compression on the new ZFS pool:

$ sudo zfs set compression=lz4 mypool

Verify compression by checking the compression ratio:

$ zfs get compression,compressratio mypool

2. Enable Deduplication (Optional): Deduplication can be enabled if necessary for the environment. However, it is memory-intensive and should be used with caution:

$ sudo zfs set dedup=on mypool

3. Set Additional Pool Properties: Configure other necessary pool properties, such as encryption, quotas, or adjusting the mount points to fit the needs of the system.

Step 4: Verifying and Scrubbing the ZFS Pool

1. Check Pool Status: Ensure that the pool is functioning correctly by checking its status:

$ sudo zpool status

2. Scrub the Pool: Perform a scrub to check the integrity of the data in the pool:

$ sudo zpool scrub mypool

A scrub reads through all the data, verifies checksums, and corrects any errors using the pool’s redundancy.

Step 5: Post-Migration Cleanup

After ensuring the data has been successfully migrated and the ZFS pool is operating correctly, the LVM volumes can be unmounted, and the partitions can be repurposed.

1. Unmount the LVM Volume:

$ sudo umount /mnt/lvm

2. Reclaim or Reformat the LVM Partition: Use fdisk, parted, or similar tools to delete or reformat the old LVM partitions as necessary.

LVM to ZFS Command and Utility Mapping