Software RAID Installation

Software RAID provides improved performance and/or reliability through redundancy. While Lunar Linux doesn't yet have an automated RAID setup in the installer, configuring RAID manually is straightforward.

Overview

Software RAID allows you to combine multiple physical disks into logical arrays that provide:

RAID 0: Striping for improved performance
RAID 1: Mirroring for redundancy
RAID 5/6: Striping with parity for both performance and redundancy
RAID 10: Combination of mirroring and striping

This guide focuses on RAID 1 (mirroring) as an example, but the principles apply to other RAID levels.

Step 1: Boot the ISO

Boot from the Lunar ISO
Complete initial setup (language, locale, keyboard)
Switch to virtual console 2 (VC/2) using Ctrl+Alt+F2
Begin manual RAID configuration

Step 2: Partition Your Disks

The easiest approach for partition-based RAID is to partition one disk, then copy the layout to the others.

Partition the First Disk

cfdisk /dev/hda

Important: Set your partition type to Linux raid autodetect (0xfd). This is essential for the system to recognize and boot from RAID partitions.

Replicate Partition Layout

Copy the partition table to your second disk using sfdisk:

cd /tmp
sfdisk -d /dev/hda > dump
sfdisk /dev/hdb < dump

This creates an identical partition layout on /dev/hdb, which is especially useful for RAID 1 setups.

For RAID arrays with more disks:

sfdisk /dev/hdc < dump
sfdisk /dev/hdd < dump

Step 3: Create RAID Configuration

Create a RAID configuration file in /tmp/raidtab:

Example: RAID 1 Configuration

raiddev         /dev/md0
raid-level      1
nr-raid-disks   2
nr-spare-disks  0
persistent-superblock 1
chunk-size      32
device          /dev/hda1
raid-disk       0
device          /dev/hdb1
raid-disk       1

Configuration Parameters Explained

raiddev: The RAID device name (e.g., /dev/md0)
raid-level: RAID level (0=stripe, 1=mirror, 5=stripe with parity)
nr-raid-disks: Number of active disks in the array
nr-spare-disks: Number of hot spare disks
persistent-superblock: Enables storing RAID metadata on disks
chunk-size: Size of data chunks in KB (affects performance)
device: Physical partition to include in the array
raid-disk: Position of this disk in the array

Multiple RAID Devices

You can create multiple RAID arrays for different partitions. For example:

# Boot partition
raiddev         /dev/md0
raid-level      1
nr-raid-disks   2
nr-spare-disks  0
persistent-superblock 1
chunk-size      32
device          /dev/hda1
raid-disk       0
device          /dev/hdb1
raid-disk       1

# Root partition
raiddev         /dev/md1
raid-level      1
nr-raid-disks   2
nr-spare-disks  0
persistent-superblock 1
chunk-size      32
device          /dev/hda2
raid-disk       0
device          /dev/hdb2
raid-disk       1

Step 4: Initialize the RAID Device

Create and start the RAID array:

mkraid --really-force --configfile /tmp/raidtab /dev/md0

The --really-force flag bypasses safety checks. Use with caution.

Monitor Sync Progress

RAID 1 and higher levels need to synchronize data across disks:

cat /proc/mdstat

Example output:

Personalities : [raid1]
md0 : active raid1 hdb1[1] hda1[0]
      104320 blocks [2/2] [UU]
      [====>................]  resync = 23.4% (24448/104320) finish=0.5min speed=2444K/sec

Step 5: Format the RAID Filesystem

You can format and work with RAID devices while they're syncing, though performance may be reduced:

mkfs.ext3 /dev/md0
mkfs.ext3 /dev/md1
mkfs.ext3 /dev/md2

Recommendation: Wait for the sync to complete before proceeding. This ensures no bad sectors exist and the array is functioning correctly.

Step 6: Save Your Configuration

Save the RAID configuration to the array itself for future use:

# Mount the root RAID device
mount /dev/md0 /mnt

# Create etc directory
mkdir /mnt/etc

# Copy configuration
cp /tmp/raidtab /mnt/etc/raidtab

# Unmount
umount /mnt

Important: Since /tmp is in RAM, your configuration will be lost on reboot if you don't save it.

Step 7: Install Lunar

Now use the Lunar installer to complete the installation:

Return to the installer interface
In the partition selection menu, choose Add device
Enter your RAID device manually (e.g., /dev/md0)
Do NOT format if you already formatted in Step 5
Select the correct filesystem type
Assign mount points (e.g., /, /boot, /home)
Continue with the normal installation process

Step 8: Configure Bootloader

LILO Configuration

LILO can boot directly from software RAID. Configure /etc/lilo.conf:

# Boot from the physical drive
boot = /dev/hda

# Root filesystem on RAID
root = /dev/md2

Important: The boot parameter should point to a physical drive (/dev/hda), not the RAID device, while root points to your RAID root partition.

Enhanced LILO Configuration (Recommended)

For better reliability, install LILO to multiple drive MBRs:

raid-extra-boot=/dev/hda,/dev/hdb
boot = /dev/md0
root = /dev/md1

This writes the bootloader to both hard drive MBRs, ensuring you can boot even if one drive fails.

GRUB Configuration

GRUB can read from underlying RAID partitions (but not stripe-based RAID):

default 0
timeout 30
color white/blue white/black

title Lunar Linux
root (hd0,0)
kernel /vmlinuz root=/dev/md1

Note: GRUB reads from one physical partition, so this won't work with RAID 0 (striping).

Legacy BIOS Considerations

Older BIOSes may require physical disk parameters. See the Software RAID HOWTO for details.

Verifying Your RAID Array

After installation and reboot, verify your RAID array:

# Check array status
cat /proc/mdstat

# Detailed information
mdadm --detail /dev/md0

Managing Your RAID Array

Adding a Spare Disk

mdadm --add /dev/md0 /dev/hdc1

Removing a Failed Disk

mdadm --fail /dev/md0 /dev/hdb1
mdadm --remove /dev/md0 /dev/hdb1

Stopping an Array

mdadm --stop /dev/md0

Starting an Array

mdadm --assemble /dev/md0 /dev/hda1 /dev/hdb1

Troubleshooting

Array Won't Assemble at Boot

Ensure /etc/mdadm.conf exists and contains your array configuration:

mdadm --detail --scan > /etc/mdadm.conf

Bootloader Won't Install

Verify:

Partition type is set to 0xfd (Linux raid autodetect)
Boot partition is marked as bootable/active
LILO configuration uses correct device names

Poor Performance

Increase chunk-size in raidtab (typical values: 32KB-256KB)
Enable write-behind for RAID 1 to improve write performance
Consider RAID 10 instead of RAID 5 for better write performance