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+OpenWrt 24.x Extroot on XE300
+
+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
+
+OpenWrt 24.x, fresh flash
+
+SD card in the built‑in slot
+
+The card appears as /dev/sda with one partition /dev/sda1
+
+You don’t care about any 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).
+
+Install the packages that make extroot possible:
+
+opkg update
+opkg install block-mount kmod-fs-ext4 kmod-usb-storage e2fsprogs
+
+
+What they do:
+
+block-mount – block info, fstab handling, extroot logic
+
+kmod-fs-ext4 – kernel driver for ext4 filesystem
+
+kmod-usb-storage – makes the SD slot show up as /dev/sda
+
+e2fsprogs – gives you mkfs.ext4
+
+2. Confirm the SD card is detected as /dev/sda//dev/sda1
+
+Check dmesg:
+
+dmesg | grep -i sd
+
+
+On your XE300 you should see something like:
+
+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:
+
+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.
+
+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)”
+
+Answer 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.
+
+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 $UUID
+
+
+You should see a UUID like:
+
+4851f00e-696b-47d3-a529-82c2aca292db
+
+
+Now write the minimal extroot config via UCI:
+
+uci set fstab.extroot="mount"
+uci set fstab.extroot.uuid="$UUID"
+uci set fstab.extroot.target="/overlay"
+uci set fstab.extroot.fstype="ext4"
+uci set fstab.extroot.enabled="1"
+uci commit fstab
+
+
+Sanity‑check the file:
+
+cat /etc/config/fstab
+
+
+Expected content (plus the global section):
+
+config global
+        option anon_swap '0'
+        option anon_mount '0'
+        option auto_swap '1'
+        option auto_mount '1'
+        option delay_root '5'
+        option check_fs '0'
+
+config mount 'extroot'
+        option uuid '4851f00e-696b-47d3-a529-82c2aca292db'
+        option target '/overlay'
+        option fstype 'ext4'
+        option enabled '1'
+
+
+Note what’s not there:
+
+No /rwm mount
+
+No copy of internal overlay
+
+This is intentionally a clean, single‑overlay setup that lives entirely on the SD card.
+
+5. Reboot into extroot
+reboot
+
+
+Let the router come back up and SSH in again.
+
+6. Verify that the SD card is now your root overlay
+
+Run:
+
+df -h
+
+
+On your working system, you got:
+
+Filesystem           Size  Used Available Use% Mounted on
+/dev/root            4.0M  4.0M        0 100% /rom
+tmpfs               58.7M  200.0K    58.5M  0% /tmp
+/dev/sda1          468.3G  2.1M     444.4G  0% /overlay
+overlayfs:/overlay  468.3G  2.1M     444.4G  0% /
+
+
+Interpreting that:
+
+/dev/root at /rom → the read‑only squashfs from flash (normal)
+
+/dev/sda1 mounted at /overlay → SD card is the writable layer
+
+overlayfs:/overlay mounted on / → your whole root filesystem is now the 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:
+
+mount | grep sda1
+mount | grep overlay
+
+
+Should show:
+
+/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.
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