Mastering Linux Storage: Why You Should Use UUIDs

When we attach a new raw disk to a Linux system, we can’t just start storing files on it right away. At first, the disk shows up as a block device under /dev/, but it’s completely uninitialized.

The Workflow: Disk → Partition → Format (Filesystem) → Mount → Use

1. View Your Disks

First use lsblk or fdisk -l to see all our disks:

sda        8:0    0  30G     0  disk
├─ sda1    8:1    0  29.9G   0  part /
└─ sda15  8:15   0  106M   0  part /boot/efi
sdb       8:16  0  4G      0  disk

New disk shows up as sdb (could be sdc, sdd..). But right now, it’s just a block of raw space. We can’t use it yet.

2. Partition the Disk

Partitioning is basically “carving” the disk into usable slices. We’ll use fdisk to create a single partition:

sudo fdisk /dev/sdb

Choose n for new, p for primary, accept the defaults, then w to write changes.

Now lsblk shows:

sdb     8:16 0 4G 0 disk
└─sdb1 8:17 0 4G 0 part

3. Format & Mount the Partition

Use sudo mkfs.ext4 /dev/sdb1 to format the partition in ext4 file system.

In Linux, everything is a file, and the whole system is a single directory tree rooted at /. Disks don’t “appear” on their own; we must mount them into this tree.

sudo mkdir -p /mnt/datadisk1
sudo mount /dev/sdb1 /mnt/datadisk1

Verify via df -h.

4. The Reboot Trap

Manual mounts vanish after a reboot. To make it permanent, you might add a line to /etc/fstab:

/dev/sdb1 /mnt/datadisk1 ext4 defaults 0 2

All good… RIGHT? Wrong.

After rebooting, the disk order might change. My 4 GB disk could become /dev/sda and my OS disk /dev/sdb. Suddenly, my entire root filesystem gets mounted into /mnt/datadisk1. 😭

5. The Fix: Use UUIDs Instead

Every partition gets a UUID (Universally Unique Identifier) when it’s formatted. It’s written into the filesystem metadata and doesn’t change even if the device name does.

You can see it with:

sudo blkid /dev/sda1

Instead of using /dev/sdb1 in /etc/fstab, use the UUID:

UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx /mnt/datadisk1 ext4 defaults 0 2

Remount and our data is back, and now it’ll stay mounted correctly across reboots! 🥳

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If you’re new to managing storage on Linux, I hope this saves you a couple of reboots and a mild heart attack 🫶