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Formatting

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Scott Leonard
2025-11-22 11:36:47 -08:00
parent 3aca926512
commit 871f1d1b68
1 changed files with 47 additions and 64 deletions
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extroot.txt
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@@ -1,27 +1,26 @@
OpenWrt 24.x Extroot on XE300
Goal: Use a 512 GB microSD card as the router’s writable storage (overlay),
Goal: Use a 512 GB microSD card as the router's writable storage (overlay),
single ext4 partition, no data copied from internal flash.
Assumptions (based on your box):
Device: GL‑iNet XE300
Device: GL-iNet XE300
OpenWrt 24.x, fresh flash
OpenWrt: 24.x, fresh flash
SD card in the built‑in slot
SD card location: built-in slot
The card appears as /dev/sda with one partition /dev/sda1
Detected as: /dev/sda with one partition /dev/sda1
You don’t care about any existing data on the card or in the old overlay
Overlay: You don't care about existing data on the card or in the old overlay
1. Insert card & install required packages
Insert the microSD card.
SSH into the router (root@192.168.x.x, etc).
SSH into the router (root@192.168.x.x etc).
Install the packages that make extroot possible:
Install the extroot-related packages:
opkg update
opkg install block-mount kmod-fs-ext4 kmod-usb-storage e2fsprogs
@@ -29,65 +28,58 @@ opkg install block-mount kmod-fs-ext4 kmod-usb-storage e2fsprogs
What they do:
block-mount – block info, fstab handling, extroot logic
block-mount - block info, fstab handling, extroot logic
kmod-fs-ext4 – kernel driver for ext4 filesystem
kmod-fs-ext4 - kernel driver for ext4 filesystem
kmod-usb-storage – makes the SD slot show up as /dev/sda
kmod-usb-storage - makes the SD slot show up as /dev/sda
e2fsprogs – gives you mkfs.ext4
e2fsprogs - provides mkfs.ext4
2. Confirm the SD card is detected as /dev/sda//dev/sda1
2. Confirm the SD card is /dev/sda and /dev/sda1
Check dmesg:
dmesg | grep -i sd
On your XE300 you should see something like:
On the XE300 you should see:
sd 0:0:0:0: [sda] 1000005632 512-byte logical blocks: (512 GB/477 GiB)
sda: sda1
sd 0:0:0:0: [sda] Attached SCSI removable disk
That tells you:
This tells you:
Disk: /dev/sda
Partition already present: /dev/sda1
If you don’t see sda1 for some reason in the future, you’d need to create a partition—but on your current setup, it’s there already, so we can jump straight to formatting.
If /dev/sda1 is missing, you'd need to partition manually. In your case, it exists already.
3. Format /dev/sda1 as ext4 for extroot
We’re going to erase whatever is on that partition and build a fresh ext4 FS.
mkfs.ext4 -L extroot /dev/sda1
You may get a warning like “contains an exfat file system – Proceed anyway? (y,N)”
If you get a warning like “contains an exfat file system - Proceed anyway? (y,N)”, type:
Answer y
y
You should see output about creating the filesystem, ending with success and a UUID.
At this point /dev/sda1 is a clean ext4 filesystem labeled extroot.
You should see output ending with success and a UUID.
4. Grab the UUID and create the extroot fstab entry
Ask OpenWrt’s block layer for info and capture the UUID:
UUID=$(block info | awk -F\" '/sda1/ {print $2}')
echo $UUID
You should see a UUID like:
Sample UUID output:
4851f00e-696b-47d3-a529-82c2aca292db
Now write the minimal extroot config via UCI:
Now write the minimal extroot config using uci:
uci set fstab.extroot="mount"
uci set fstab.extroot.uuid="$UUID"
@@ -97,12 +89,12 @@ uci set fstab.extroot.enabled="1"
uci commit fstab
Sanity‑check the file:
Sanity-check the file:
cat /etc/config/fstab
Expected content (plus the global section):
Expected output:
config global
option anon_swap '0'
@@ -119,28 +111,24 @@ config mount 'extroot'
option enabled '1'
Note what’s not there:
Not included:
No /rwm mount
No copy of internal overlay
This is intentionally a clean, single‑overlay setup that lives entirely on the SD card.
This is a clean, SD-only overlay setup.
5. Reboot into extroot
reboot
Let the router come back up and SSH in again.
Wait for the router to come back up, then SSH in again.
6. Verify that the SD card is now your root overlay
Run:
df -h
On your working system, you got:
Expected output:
Filesystem Size Used Available Use% Mounted on
/dev/root 4.0M 4.0M 0 100% /rom
@@ -149,34 +137,29 @@ tmpfs 58.7M 200.0K 58.5M 0% /tmp
overlayfs:/overlay 468.3G 2.1M 444.4G 0% /
Interpreting that:
Explanation:
/dev/root at /rom → the read‑only squashfs from flash (normal)
/dev/root at /rom → read-only squashfs from flash
/dev/sda1 mounted at /overlay → SD card is the writable layer
/dev/sda1 at /overlay → SD card is the writable layer
overlayfs:/overlay mounted on / → your whole root filesystem is now the ROM + SD overlay
overlayfs:/overlay on / → full rootfs = ROM + SD overlay
That’s exactly what we want: the router is effectively a 468 GB OpenWrt box.
Extra checks if you ever want them:
You now have a 468 GB OpenWrt box.
Extra checks (optional)
mount | grep sda1
mount | grep overlay
Should show:
Should return:
/dev/sda1 on /overlay type ext4
overlayfs:/overlay on / type overlay
7. Quick functional test
Just to flex:
opkg install tcpdump
df -h /overlay
You’ll see a tiny bump in “Used” on /dev/sda1, confirming packages are being installed to SD‑backed overlay, not the tiny internal flash.
You should see a small increase in Used for /dev/sda1, proving packages are installed to SD-backed overlay—not internal flash.