Ever added a new disk to your server only to find it playing hide-and-seek with your system? 🙈 Or perhaps you’ve hot-swapped a drive and now you’re wondering how to make Linux acknowledge its existence without the dreaded reboot? ⚡️ Well, grab your magnifying glass because today we’re becoming disk detectives! 🕵️‍♀️💾

The Case of the Invisible Disk 👻💿

When you connect a new disk to your Linux system, sometimes it doesn’t show up automatically. This isn’t because your system is being stubborn—it’s just that Linux needs a little nudge to scan for new hardware. 🔄

Your Detective Toolkit 🧰🛠️

The command you shared is actually a powerful tool in our disk detection arsenal:

# Scan a specific host controller
echo "- - -" > /sys/class/scsi_host/host0/scan

# Or scan ALL host controllers (recommended)
for host in /sys/class/scsi_host/*; do
  echo "- - -" | tee $host/scan
  ls /dev/sd*
done

# Rescan a specific disk that's already detected
echo "1" > /sys/class/block/sdb/device/rescan

Breaking Down the Clues 🧩🔎

What’s happening here? Let’s decode this like proper detectives:

The magic string "- - -" tells the system to scan all channels, all targets, and all LUNs (Logical Unit Numbers) on that host controller. It’s like telling your system, “Check everywhere, leave no storage unturned!” 🧹🔍

The for loop visits each SCSI host controller in your system—these are the pathways to your storage devices. By scanning each one, we’re covering all possible connections. 🌐🔄

After each scan, the ls /dev/sd* command shows us which disk devices are currently detected, giving us immediate feedback on our investigation. 📋✅

The last command is for when a disk is already visible but might have changed—perhaps it’s grown in size after being expanded in a virtual environment or SAN. This tells the system to take another look at a specific disk. 🔄📏

When to Use These Incantations ✨⚡️

• After physically adding a new hard drive 🔌💽
• After adding a virtual disk in a VM 💻➕
• After resizing a disk in your virtual environment or SAN 📏↔️
• When a disk mysteriously disappears (it happens to the best of us!) 👻💾

Success! Case Closed 🎉🏆

If all goes well, your new disk should appear in the /dev/sd* list. Now you can format it, partition it, and bring it into your storage pool—ready to store more cat pictures 😺, cryptocurrency wallets 💰, or that novel you’ve been meaning to write! ✍️📚

Remember: Being a good disk detective means you can solve storage mysteries without the hassle of rebooting your system. Now go forth and detect those disks with confidence! 🚀💾