Working with physical USB drives for creating bootable images introduces several inefficiencies:

• Manual insertion/removal cycles
• Limited by USB transfer speeds
• Wear on physical media
• Potential for device misidentification (/dev/sdx vs /dev/sdy)

Linux provides several methods to create block devices in RAM. Let's examine the most practical approaches:

Method 1: Using the brd (RAM Disk) Module

First, load the brd kernel module with custom size parameters:

sudo modprobe brd rd_nr=1 rd_size=$((512 * 1024))

This creates a 512MB RAM disk at /dev/ram0. Now we can partition it:

sudo sfdisk /dev/ram0 << EOF
,20000,c
,1000000,83
EOF

Method 2: Using dmsetup with a Loopback

For more flexibility, we can use device-mapper:

# Create a RAM-backed file
sudo mount -t tmpfs -o size=520M tmpfs /mnt/ramdisk
dd if=/dev/zero of=/mnt/ramdisk/disk.img bs=1M count=520

# Set up loop device
sudo losetup -f /mnt/ramdisk/disk.img
LOOP_DEV=$(losetup -a | grep disk.img | awk -F: '{print $1}')

# Partition the loop device
sudo sfdisk $LOOP_DEV << EOF
,20000,c
,1000000,83
EOF

# Refresh partition table
sudo partprobe $LOOP_DEV

Here's a full script that creates a RAM-based image and prepares it exactly like your USB process:

#!/bin/bash

# Parameters
IMAGE_SIZE_MB=520
FAT32_SIZE_SECTORS=20000
EXT3_SIZE_SECTORS=1000000
OUTPUT_IMAGE="usb.img"

# Create RAM disk
sudo modprobe brd rd_nr=1 rd_size=$((IMAGE_SIZE_MB * 1024))
RAMDISK="/dev/ram0"

# Partition
sudo sfdisk $RAMDISK << EOF
,$FAT32_SIZE_SECTORS,c
,$EXT3_SIZE_SECTORS,83
EOF

# Refresh partitions
sudo partprobe $RAMDISK

# Format
sudo mkfs.vfat ${RAMDISK}1
sudo mkfs.ext3 ${RAMDISK}2

# Mount and populate partitions
FAT_MOUNT=$(mktemp -d)
EXT_MOUNT=$(mktemp -d)

sudo mount ${RAMDISK}1 $FAT_MOUNT
sudo mount ${RAMDISK}2 $EXT_MOUNT

# Copy your files (example)
sudo cp kernel.bin $FAT_MOUNT/
sudo cp startup.script $FAT_MOUNT/
sudo tar xzf rootfs.tar.gz -C $EXT_MOUNT/

# Unmount
sudo umount $FAT_MOUNT
sudo umount $EXT_MOUNT
rmdir $FAT_MOUNT $EXT_MOUNT

# Create final image
sudo dd if=$RAMDISK of=$OUTPUT_IMAGE bs=1M count=$IMAGE_SIZE_MB

# Clean up
sudo rmmod brd

# Compress
gzip $OUTPUT_IMAGE

Testing with a 520MB image:

For production environments, consider these enhancements:

1. Add error checking at each step
2. Implement logging
3. Create systemd service for persistent RAM disks
4. Add checksum verification

Problem: "Cannot create partitions - device busy"
Solution: Ensure no processes are mounting the partitions and use partprobe after partitioning.

Problem: "RAM disk too small"
Solution: Check available RAM with free -h and adjust size parameters accordingly.

When developing bootable USB images in Linux, the traditional physical device workflow presents several inefficiencies:

1. Manual USB insertion/removal cycles
2. Physical wear on flash storage
3. Slower read/write speeds compared to RAM
4. Potential cross-contamination between test runs

After extensive testing, I've found these reliable approaches for creating flexible block devices in RAM:

# Load the brd kernel module with custom size (in pages, default 4KB each)
sudo modprobe brd rd_nr=1 rd_size=524288  # Creates 2GB RAM disk at /dev/ram0

# Alternative using loop devices with tmpfs:
mkdir -p /mnt/tmpdisk
mount -t tmpfs -o size=520M tmpfs /mnt/tmpdisk
truncate -s 520M /mnt/tmpdisk/disk.img
sudo losetup --find --show /mnt/tmpdisk/disk.img  # Returns /dev/loopX

Here's my production-grade script for RAM-based image creation:

#!/bin/bash
set -e

# 1. Create RAM device
DEV=$(sudo losetup --find --show /mnt/tmpdisk/disk.img)

# 2. Partitioning
sudo sfdisk "${DEV}" << EOF
,10M,c
,500M,83
EOF

# 3. Format partitions
sudo mkfs.vfat "${DEV}p1"
sudo mkfs.ext3 "${DEV}p2"

# 4. Mount and populate
mkdir -p /mnt/{boot,root}
sudo mount "${DEV}p1" /mnt/boot
sudo mount "${DEV}p2" /mnt/root

# 5. Copy files (example)
sudo cp -r ./kernel/* /mnt/boot/
sudo rsync -a ./rootfs/ /mnt/root/

# 6. Create final image
sudo dd if="${DEV}" of=./output.img bs=1M count=510 status=progress

# Cleanup
sync
sudo umount /mnt/{boot,root}
sudo losetup -d "${DEV}"

Benchmark results (average of 10 runs on Ryzen 7 5800X):

Critical safeguards to implement:

# Check available RAM before allocation
REQ_MB=520
AVAIL_MB=$(free -m | awk '/Mem:/ {print $7}')
if [ "$AVAIL_MB" -lt "$((REQ_MB + 200))" ]; then
    echo "Error: Insufficient RAM" >&2
    exit 1
fi

# Verify partition alignment
sudo parted "${DEV}" align-check optimal 1 || {
    echo "Partition alignment error" >&2
    exit 1
}

For persistent setups, create a service unit:

# /etc/systemd/system/ramdisk.service
[Unit]
Description=RAM Disk for Image Testing
Before=multi-user.target

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/usr/bin/bash -c " \
    mkdir -p /mnt/tmpdisk && \
    mount -t tmpfs -o size=520M tmpfs /mnt/tmpdisk && \
    truncate -s 520M /mnt/tmpdisk/disk.img && \
    losetup --find --show /mnt/tmpdisk/disk.img"

ExecStop=/usr/bin/bash -c " \
    LOOP=$(losetup -j /mnt/tmpdisk/disk.img | cut -d: -f1) && \
    [ -n \"$LOOP\" ] && losetup -d \"$LOOP\"; \
    umount /mnt/tmpdisk"

[Install]
WantedBy=multi-user.target