A comprehensive guide to changing NVMe device formats, adjusting block sizes, and managing namespaces on Linux systems.

Overview

NVMe devices support multiple format configurations, including different block sizes (512B, 4KB, etc.) and metadata settings. This guide covers how to safely change these formats.

Prerequisites

  • NVMe device installed in your system
  • Root or sudo access
  • nvme-cli tools installed
  • WARNING: Formatting will destroy all data on the device

Installation

Install NVMe CLI Tools

Ubuntu/Debian:

sudo apt update
sudo apt install nvme-cli

RHEL/CentOS/Fedora:

sudo dnf install nvme-cli

Identifying Your NVMe Device

List NVMe Devices

# List all NVMe devices
sudo nvme list

# Example output:
# Node             SN                   Model                Version  Namespace Usage        Format
# ---------------- -------------------- -------------------- -------- --------- ------------ ------
# /dev/nvme0n1     S123ABC456789        Samsung SSD 980 PRO  1.0      1         500.11  GB / 500.11  GB  512 B + 0 B

Get Device Information

# Get detailed device info
sudo nvme id-ctrl /dev/nvme0

# Get namespace info
sudo nvme id-ns /dev/nvme0n1

Viewing Supported Formats

Check Available Formats

sudo nvme id-ns /dev/nvme0n1 -H | grep "LBA Format"

Example output:

LBA Format  0 : Metadata Size: 0   bytes - Data Size: 512 bytes - Relative Performance: 0x2 Good
LBA Format  1 : Metadata Size: 0   bytes - Data Size: 4096 bytes - Relative Performance: 0x1 Better

Changing NVMe Format

Backup Your Data

CRITICAL: Always backup data before formatting!

# Example backup (if filesystem is mounted)
sudo dd if=/dev/nvme0n1 of=/path/to/backup.img bs=4M status=progress

Format Command Syntax

sudo nvme format /dev/nvme0n1 --lbaf=<format_id>

Parameters:

  • --lbaf=<id>: LBA Format index (0, 1, 2, etc.)
  • --ses=0: No secure erase
  • --ses=1: User data erase
  • --ses=2: Cryptographic erase

Example: Change to 4KB Block Size

# Format to 4KB blocks (typically lbaf=1)
sudo nvme format /dev/nvme0n1 --lbaf=1 --ses=1

# Verify the format
sudo nvme id-ns /dev/nvme0n1 -H | grep "in use"

Example: Change to 512B Block Size

# Format to 512B blocks (typically lbaf=0)
sudo nvme format /dev/nvme0n1 --lbaf=0 --ses=1

Advanced: Namespace Management

Delete Namespace

# Delete namespace 1
sudo nvme delete-ns /dev/nvme0 -n 1

Create New Namespace

# Create namespace with specific block size
sudo nvme create-ns /dev/nvme0 --nsze=<size_in_blocks> --ncap=<capacity> --flbas=<format>

# Example: Create 100GB namespace with 4KB blocks
sudo nvme create-ns /dev/nvme0 --nsze=26214400 --ncap=26214400 --flbas=1

Attach Namespace

# Attach namespace to controller
sudo nvme attach-ns /dev/nvme0 -n 1 -c 0

Verification

Verify Format Change

# Check current format
sudo nvme id-ns /dev/nvme0n1 -H | grep -A5 "LBA Format"

# Check block size
sudo blockdev --getbsz /dev/nvme0n1

# Verify device is ready
sudo nvme list

Test the Device

# Write test pattern
sudo dd if=/dev/zero of=/dev/nvme0n1 bs=1M count=100 status=progress

# Read test
sudo dd if=/dev/nvme0n1 of=/dev/null bs=1M count=100 status=progress

Troubleshooting

Format Command Fails

Issue: Format command returns error

Solutions:

# Check if device is mounted (unmount if necessary)
mount | grep nvme0n1
sudo umount /dev/nvme0n1

# Check if device is in use
lsof | grep nvme0n1
fuser -v /dev/nvme0n1

# Ensure no LVM/RAID is using the device
sudo pvs
sudo mdadm --detail --scan

Namespace Issues

Issue: Cannot delete or modify namespace

Solutions:

# Detach namespace first
sudo nvme detach-ns /dev/nvme0 -n 1 -c 0

# Then delete
sudo nvme delete-ns /dev/nvme0 -n 1

# Reset NVMe subsystem (last resort)
sudo nvme reset /dev/nvme0

Performance After Format

Issue: Poor performance after changing format

Check alignment:

# Check filesystem alignment
sudo parted /dev/nvme0n1 align-check optimal 1

# Recreate filesystem with proper alignment
sudo mkfs.ext4 -b 4096 /dev/nvme0n1

Best Practices

  1. Always backup data before any format operation
  2. Verify supported formats using nvme id-ns before formatting
  3. Use 4KB blocks for modern systems (better performance)
  4. Align filesystems to match the LBA format
  5. Test after formatting to ensure stability
  6. Document your configuration for future reference

Common Use Cases

Converting Legacy 512B to 4KB

# 1. Backup data
sudo dd if=/dev/nvme0n1 of=/backup/nvme-backup.img bs=4M

# 2. Format to 4KB
sudo nvme format /dev/nvme0n1 --lbaf=1 --ses=1

# 3. Create aligned partition
sudo parted /dev/nvme0n1 --align optimal mklabel gpt
sudo parted /dev/nvme0n1 --align optimal mkpart primary 0% 100%

# 4. Create filesystem with 4KB blocks
sudo mkfs.ext4 -b 4096 /dev/nvme0n1p1

Secure Erase and Reformat

# Cryptographic erase and format to 4KB
sudo nvme format /dev/nvme0n1 --lbaf=1 --ses=2

# Verify secure erase completed
sudo nvme smart-log /dev/nvme0 | grep "percentage_used"

Important Warnings

⚠️ Data Loss: Formatting destroys all data on the device ⚠️ No Undo: Format operations cannot be reversed ⚠️ Device Compatibility: Not all devices support all formats ⚠️ System Disruption: Never format a device in use by the system

Additional Resources

Summary

Changing NVMe format is straightforward but requires careful attention to:

  • Backing up data
  • Verifying supported formats
  • Proper secure erase selection
  • Post-format verification

Always test the new configuration thoroughly before putting the device into production use.

© 2025 Darren Soothill. All rights reserved.