Linux Disk and Storage Management Explained — Partitions, LVM and Real-World Patterns

#!/bin/bash
# inspect_disk_landscape.sh
# Safe read-only commands to fully understand your storage before making any changes.
# Run as root (or with sudo) for full output.

echo "=== BLOCK DEVICE TREE (lsblk) ==="
# Shows all block devices, their sizes, types, and mount points.
# NAME: device name | SIZE: total size | TYPE: disk/part/lvm | MOUNTPOINT: where it's mounted
lsblk -o NAME,SIZE,TYPE,FSTYPE,MOUNTPOINT,UUID

echo ""
echo "=== PARTITION DETAILS (fdisk) ==="
# fdisk -l lists every partition on every disk with sector info and partition type.
# This is the authoritative view of what's physically on the disk.
sudo fdisk -l /dev/sda

echo ""
echo "=== MOUNTED FILESYSTEM USAGE (df) ==="
# df -h shows only MOUNTED filesystems with human-readable sizes.
# Use this to see actual disk usage — not just what exists.
df -h --output=source,size,used,avail,pcent,target

echo ""
echo "=== FILESYSTEM UUIDs (blkid) ==="
# blkid reads filesystem metadata — UUID, TYPE, LABEL.
# Always use UUID in /etc/fstab — never /dev/sdX names.
sudo blkid

#!/bin/bash
# partition_format_mount.sh
# Full walkthrough: take a raw disk (/dev/sdb) and make it usable.
# WARNING: This DESTROYS all data on /dev/sdb. Verify the device name first.
# Prerequisites: run as root. Confirm target disk with: lsblk | grep sdb

TARGET_DISK="/dev/sdb"           # The raw disk we're preparing
PARTITION="/dev/sdb1"            # The partition we'll create
MOUNT_DIR="/mnt/appdata"         # Where we'll attach it in the filesystem tree
FS_LABEL="appdata-vol"           # Human-readable label (helpful in logs and blkid)

# --- STEP 1: PARTITION THE DISK ---
# gdisk creates a GPT partition table (correct for disks > 2TB and modern systems).
# We feed commands via heredoc to automate the interactive prompt:
#   n = new partition | 1 = partition number | defaults for start/end (use whole disk)
#   8300 = Linux filesystem partition type code | w = write and exit
echo "Creating GPT partition table on ${TARGET_DISK}..."
sudo gdisk ${TARGET_DISK} <<EOF
n
1


8300
w
yes
EOF

# Inform the kernel about the new partition layout without rebooting.
# partprobe reads the new partition table and updates the kernel's view.
sudo partprobe ${TARGET_DISK}
sleep 2   # Brief pause — kernel needs a moment to register the new partition

# Confirm the partition was created
echo "Partition layout after gdisk:"
lsblk ${TARGET_DISK}

# --- STEP 2: FORMAT THE PARTITION ---
# mkfs.ext4 writes an ext4 filesystem into the partition.
# -L sets a human-readable label — visible in lsblk, blkid, and system logs.
# This step is IRREVERSIBLE on a partition with existing data.
echo "Formatting ${PARTITION} as ext4..."
sudo mkfs.ext4 -L ${FS_LABEL} ${PARTITION}

# --- STEP 3: CREATE MOUNT POINT ---
# The mount directory must exist before you can mount anything to it.
# mkdir -p creates it (and any missing parents) without erroring if it exists.
sudo mkdir -p ${MOUNT_DIR}

# --- STEP 4: MOUNT TEMPORARILY (to verify it works) ---
# mount attaches the filesystem — but this survives only until next reboot.
sudo mount ${PARTITION} ${MOUNT_DIR}
echo "Temporary mount successful. Testing write access..."
echo "storage_test" | sudo tee ${MOUNT_DIR}/write_test.txt > /dev/null

# --- STEP 5: GET UUID FOR FSTAB ---
# Never put /dev/sdb1 in fstab. Get the stable UUID instead.
DISK_UUID=$(sudo blkid -s UUID -o value ${PARTITION})
echo "UUID for ${PARTITION}: ${DISK_UUID}"

# --- STEP 6: ADD TO /etc/fstab FOR PERSISTENT MOUNTING ---
# Backup fstab first — a broken fstab prevents the system from booting.
sudo cp /etc/fstab /etc/fstab.backup.$(date +%Y%m%d_%H%M%S)

# Append the fstab entry:
# UUID=...   /mnt/appdata   ext4   defaults,nofail   0   2
# 'nofail' means the system still boots even if this disk is missing.
# The final '2' means fsck runs on this partition after the root partition.
echo "UUID=${DISK_UUID}  ${MOUNT_DIR}  ext4  defaults,nofail  0  2" | sudo tee -a /etc/fstab

# Verify fstab is valid by mounting everything listed in it.
# If this errors, restore from backup: sudo cp /etc/fstab.backup.* /etc/fstab
sudo mount -a && echo "fstab validation passed — all entries mounted successfully."

# Final check
df -h ${MOUNT_DIR}

#!/bin/bash
# lvm_setup_and_extend.sh
# Demonstrates: creating an LVM stack from scratch AND extending a full volume live.
# Scenario: web app data volume (/dev/sdc) is full. We add a new disk (/dev/sdd)
# and expand the logical volume online — zero downtime.

# ============================================================
# PART 1: BUILD AN LVM STACK ON A FRESH DISK
# ============================================================

NEW_DISK="/dev/sdc"              # Physical disk to hand to LVM
VOLUME_GROUP="webdata_vg"        # Our pool — think of it as the storage bucket
LOGICAL_VOLUME="webapp_lv"       # What the application actually uses
LV_SIZE="30G"                    # Initial size carved from the pool
MOUNT_POINT="/var/www/appdata"   # Where the app reads and writes

echo "=== STEP 1: Create Physical Volume ==="
# pvcreate writes LVM metadata to the disk, marking it as LVM-managed.
# After this, the disk belongs to LVM and should not be partitioned manually.
sudo pvcreate ${NEW_DISK}

# Verify the PV was created
sudo pvdisplay ${NEW_DISK}

echo ""
echo "=== STEP 2: Create Volume Group ==="
# vgcreate creates the storage pool and adds the PV to it.
# You can add multiple PVs at creation: vgcreate my_vg /dev/sdc /dev/sdd
sudo vgcreate ${VOLUME_GROUP} ${NEW_DISK}

# Verify the VG — note 'VG Size' shows total available storage in the pool
sudo vgdisplay ${VOLUME_GROUP}

echo ""
echo "=== STEP 3: Create Logical Volume ==="
# lvcreate carves out a chunk of the VG as a usable logical volume.
# -L specifies size | -n specifies the name
sudo lvcreate -L ${LV_SIZE} -n ${LOGICAL_VOLUME} ${VOLUME_GROUP}

# The LV is now available as a block device at this path:
# /dev/webdata_vg/webapp_lv  (also accessible via /dev/mapper/webdata_vg-webapp_lv)
echo "LV device path: /dev/mapper/${VOLUME_GROUP}-${LOGICAL_VOLUME}"

echo ""
echo "=== STEP 4: Format and Mount the Logical Volume ==="
sudo mkfs.ext4 -L webapp-data /dev/mapper/${VOLUME_GROUP}-${LOGICAL_VOLUME}
sudo mkdir -p ${MOUNT_POINT}
sudo mount /dev/mapper/${VOLUME_GROUP}-${LOGICAL_VOLUME} ${MOUNT_POINT}

# Add to fstab for persistence (using device mapper path — also stable with LVM)
DEVICE_PATH="/dev/mapper/${VOLUME_GROUP}-${LOGICAL_VOLUME}"
echo "${DEVICE_PATH}  ${MOUNT_POINT}  ext4  defaults,nofail  0  2" | sudo tee -a /etc/fstab

df -h ${MOUNT_POINT}

# ============================================================
# PART 2: EXTENDING THE VOLUME ONLINE (ZERO DOWNTIME)
# ============================================================
# Scenario: 6 months later, /var/www/appdata is at 90% capacity.
# We have a new disk /dev/sdd attached. Extend without unmounting.

EXTRA_DISK="/dev/sdd"           # New disk arriving in the system
EXTEND_BY="+50G"                # How much to add to the logical volume

echo ""
echo "=== EXTEND: Add new disk to the VG pool ==="
# pvcreate the new disk first, then vgextend adds it to our existing pool.
sudo pvcreate ${EXTRA_DISK}
sudo vgextend ${VOLUME_GROUP} ${EXTRA_DISK}

# Confirm the VG now has more free space
sudo vgs ${VOLUME_GROUP}

echo ""
echo "=== EXTEND: Grow the logical volume ==="
# lvextend grows the LV. -r flag is critical — it also resizes the filesystem
# inside the LV at the same time. Without -r, you'd have a bigger LV but
# the filesystem inside wouldn't know about the extra space.
sudo lvextend -L ${EXTEND_BY} -r /dev/mapper/${VOLUME_GROUP}-${LOGICAL_VOLUME}

# The application is still running. No unmount. No restart. Verify the new size:
df -h ${MOUNT_POINT}

#!/bin/bash
# storage_monitoring_and_diagnostics.sh
# Production-grade monitoring and diagnostics for Linux storage.
# Covers: disk usage, inode exhaustion, I/O performance, fstab validation.

echo "============================================"
echo " STORAGE HEALTH DASHBOARD"
echo "============================================"

# --- DISK SPACE BY FILESYSTEM ---
echo ""
echo "[1] DISK SPACE USAGE (human-readable)"
# -T shows filesystem type — useful for spotting unexpected tmpfs mounts eating space
df -hT --exclude-type=tmpfs --exclude-type=devtmpfs

# --- INODE USAGE — THE SILENT KILLER ---
echo ""
echo "[2] INODE USAGE — check this if you see 'No space left on device' with free space"
# PCent shows inode usage percentage. 100% means no new files can be created,
# even if gigabytes of block space remain.
df -i --exclude-type=tmpfs --exclude-type=devtmpfs

# --- FIND DIRECTORIES CONSUMING THE MOST DISK SPACE ---
echo ""
echo "[3] TOP 10 LARGEST DIRECTORIES under /var (common culprit for space issues)"
# du -s gives summary per directory. sort -rh sorts by size, largest first.
# --exclude prevents following bind mounts and getting misleading totals.
sudo du -sh /var/*/  2>/dev/null | sort -rh | head -10

# --- I/O PERFORMANCE SNAPSHOT ---
echo ""
echo "[4] DISK I/O STATISTICS (3-second sample)"
# iostat -xd: x=extended stats, d=devices only (skip CPU)
# Key columns: r/s (reads per sec), w/s (writes per sec), %util (device saturation)
# %util near 100% = storage bottleneck
sudo iostat -xd 1 3 2>/dev/null || echo "Install sysstat: sudo apt install sysstat"

# --- WHICH PROCESS IS HAMMERING DISK RIGHT NOW ---
echo ""
echo "[5] TOP I/O PROCESSES (requires iotop)"
# -b = batch mode (non-interactive) | -n 1 = one iteration | -o = only show active processes
sudo iotop -b -n 1 -o 2>/dev/null || echo "Install iotop: sudo apt install iotop"

# --- VALIDATE /etc/fstab WITHOUT REBOOTING ---
echo ""
echo "[6] FSTAB VALIDATION"
echo "Current /etc/fstab entries (non-comment lines):"
grep -v '^#' /etc/fstab | grep -v '^$' | column -t

echo ""
echo "Testing fstab by running: mount -a (mounts everything in fstab not already mounted)"
# mount -a is safe to run on a live system — it only mounts things not yet mounted.
# Any error here means your fstab has a problem that would break the next reboot.
sudo mount -a 2>&1 && echo "✓ fstab OK — all entries valid" || echo "✗ fstab ERROR — fix before rebooting!"

# --- SMART DISK HEALTH (physical drives only) ---
echo ""
echo "[7] DISK HEALTH CHECK (smartctl)"
# smartctl reads the drive's self-monitoring data.
# 'PASSED' = drive reports no hardware issues.
# 'FAILED' = replace the drive NOW before it dies completely.
sudo smartctl -H /dev/sda 2>/dev/null || echo "Install smartmontools: sudo apt install smartmontools"

# --- ALERT THRESHOLD: WARN IF ANY FILESYSTEM OVER 80% ---
echo ""
echo "[8] CAPACITY ALERTS (>80% used)"
df -h --output=source,pcent,target | awk 'NR>1 && $2+0 > 80 {
    print "ALERT: " $1 " at " $2 " capacity — mount: " $3
}' || echo "All filesystems under 80% — looking healthy."