diff --git a/iso/installer.py b/iso/installer.py
index 35cad41..65c67ec 100644
--- a/iso/installer.py
+++ b/iso/installer.py
@@ -8,6 +8,7 @@ import os
 import secrets
 import subprocess
 import sys
+import tempfile
 import threading
 import time
 
@@ -156,6 +157,7 @@ class InstallerWindow(Adw.ApplicationWindow):
         self.boot_size = None
         self.data_disk = None
         self.data_size = None
+        self.data_drive_has_timechain = False
         self.free_password = None
 
         # Root navigation view
@@ -667,11 +669,19 @@ class InstallerWindow(Adw.ApplicationWindow):
 
     def push_disk_confirm(self):
         """Show the selected drives and ask the user to type ERASE to confirm."""
+        self.data_drive_has_timechain = False
+        if self.data_disk:
+            data_path = f"/dev/{self.data_disk}"
+            self.data_drive_has_timechain = self.detect_existing_timechain_data(data_path)
+
         outer = Gtk.Box(orientation=Gtk.Orientation.VERTICAL, spacing=0)
 
         # Disk info group
         disk_group = Adw.PreferencesGroup()
-        disk_group.set_title("Drives to be erased")
+        if self.data_disk and self.data_drive_has_timechain:
+            disk_group.set_title("OS drive to be erased (data drive preserved)")
+        else:
+            disk_group.set_title("Drives to be erased")
         disk_group.set_margin_top(24)
         disk_group.set_margin_start(40)
         disk_group.set_margin_end(40)
@@ -688,12 +698,21 @@ class InstallerWindow(Adw.ApplicationWindow):
             data_row.set_subtitle(f"/dev/{self.data_disk}  —  {human_size(self.data_size)}")
             data_row.add_prefix(symbolic_icon("drive-harddisk-symbolic"))
             disk_group.add(data_row)
+            if self.data_drive_has_timechain:
+                note_row = Adw.ActionRow()
+                note_row.set_title(f"Existing Bitcoin timechain detected on /dev/{self.data_disk}")
+                note_row.set_subtitle("Data will be preserved and mounted as-is.")
+                note_row.add_prefix(symbolic_icon("emblem-ok-symbolic"))
+                disk_group.add(note_row)
 
         outer.append(disk_group)
 
         # Warning banner
         banner = Adw.Banner()
-        banner.set_title("⚠  All data on the above disk(s) will be permanently destroyed.")
+        if self.data_disk and self.data_drive_has_timechain:
+            banner.set_title("⚠  All data on the OS disk will be permanently destroyed. Existing Bitcoin data disk will be preserved.")
+        else:
+            banner.set_title("⚠  All data on the above disk(s) will be permanently destroyed.")
         banner.set_revealed(True)
         banner.set_margin_top(16)
         banner.set_margin_start(40)
@@ -775,9 +794,61 @@ class InstallerWindow(Adw.ApplicationWindow):
 
     # ── Worker: partition ─────────────────────────────────────────────────
 
+    def partition_path(self, dev_path, num):
+        return f"{dev_path}p{num}" if "nvme" in dev_path else f"{dev_path}{num}"
+
+    def detect_existing_timechain_data(self, data_path, buf=None):
+        data_p1 = self.partition_path(data_path, 1)
+        if not os.path.exists(data_p1):
+            return False
+
+        label = ""
+        for cmd in (
+            ["sudo", "lsblk", "-no", "LABEL", data_p1],
+            ["sudo", "blkid", "-o", "value", "-s", "LABEL", data_p1],
+        ):
+            proc = subprocess.run(cmd, capture_output=True, text=True)
+            if proc.returncode == 0:
+                stdout = proc.stdout.strip()
+                label = stdout.splitlines()[0] if stdout else ""
+                if label:
+                    break
+
+        if label != "BTCEcoandBackup":
+            return False
+
+        check_mount = tempfile.mkdtemp(prefix="sovran-installer-data-check-")
+        mounted = False
+        try:
+            run(["sudo", "mount", "-o", "ro", data_p1, check_mount])
+            mounted = True
+
+            has_bitcoin = os.path.isdir(f"{check_mount}/BTCEcoandBackup/Bitcoin_Node")
+            has_electrs = os.path.isdir(f"{check_mount}/BTCEcoandBackup/Electrs_Data")
+            if has_bitcoin and has_electrs:
+                if buf is not None:
+                    GLib.idle_add(
+                        append_text,
+                        buf,
+                        "=== Existing Bitcoin timechain detected on data drive — preserving data ===\n",
+                    )
+                return True
+            return False
+        except Exception as e:
+            log(f"Timechain detection failed for {data_p1} at mount/check step ({check_mount}): {e}")
+            return False
+        finally:
+            if mounted:
+                subprocess.run(["sudo", "umount", check_mount], capture_output=True, text=True)
+            subprocess.run(["sudo", "rmdir", check_mount], capture_output=True, text=True)
+
     def do_partition(self, buf):
         boot_path = f"/dev/{self.boot_disk}"
         data_path = f"/dev/{self.data_disk}" if self.data_disk else None
+        self.data_drive_has_timechain = False
+
+        if data_path:
+            self.data_drive_has_timechain = self.detect_existing_timechain_data(data_path, buf)
 
         # ── Wipe disk(s) ──
         GLib.idle_add(append_text, buf, "=== Wiping disk(s) ===\n")
@@ -785,12 +856,12 @@ class InstallerWindow(Adw.ApplicationWindow):
         run_stream(["sudo", "sgdisk", "--zap-all", boot_path], buf)
         run_stream(["sudo", "wipefs", "--all", "--force", boot_path], buf)
 
-        if data_path:
+        if data_path and not self.data_drive_has_timechain:
             run_stream(["sudo", "sgdisk", "--zap-all", data_path], buf)
             run_stream(["sudo", "wipefs", "--all", "--force", data_path], buf)
 
         run_stream(["sudo", "partprobe", boot_path], buf)
-        if data_path:
+        if data_path and not self.data_drive_has_timechain:
             run_stream(["sudo", "partprobe", data_path], buf)
 
         time.sleep(2)
@@ -806,7 +877,7 @@ class InstallerWindow(Adw.ApplicationWindow):
         time.sleep(2)
 
         # ── Partition data disk (if selected) ──
-        if data_path:
+        if data_path and not self.data_drive_has_timechain:
             GLib.idle_add(append_text, buf, "\n=== Partitioning data disk ===\n")
             run_stream(["sudo", "sgdisk",
                         "-n", "1:1M:0", "-t", "1:8300", "-c", "1:primary",
@@ -817,14 +888,14 @@ class InstallerWindow(Adw.ApplicationWindow):
 
         # ── Format partitions ──
         GLib.idle_add(append_text, buf, "\n=== Formatting partitions ===\n")
-        boot_p1 = f"{boot_path}p1" if "nvme" in boot_path else f"{boot_path}1"
-        boot_p2 = f"{boot_path}p2" if "nvme" in boot_path else f"{boot_path}2"
+        boot_p1 = self.partition_path(boot_path, 1)
+        boot_p2 = self.partition_path(boot_path, 2)
 
         run_stream(["sudo", "mkfs.vfat", "-F", "32", boot_p1], buf)
         run_stream(["sudo", "mkfs.ext4", "-F", "-L", "sovran_systemsos", boot_p2], buf)
 
-        if data_path:
-            data_p1 = f"{data_path}p1" if "nvme" in data_path else f"{data_path}1"
+        if data_path and not self.data_drive_has_timechain:
+            data_p1 = self.partition_path(data_path, 1)
             run_stream(["sudo", "mkfs.ext4", "-F", "-L", "BTCEcoandBackup", data_p1], buf)
 
         # ── Mount filesystems ──
@@ -834,7 +905,7 @@ class InstallerWindow(Adw.ApplicationWindow):
         run_stream(["sudo", "mount", "-o", "umask=0077,defaults", boot_p1, "/mnt/boot/efi"], buf)
 
         if data_path:
-            data_p1 = f"{data_path}p1" if "nvme" in data_path else f"{data_path}1"
+            data_p1 = self.partition_path(data_path, 1)
             run_stream(["sudo", "mkdir", "-p", "/mnt/run/media/Second_Drive"], buf)
             run_stream(["sudo", "mount", data_p1, "/mnt/run/media/Second_Drive"], buf)
             run_stream(["sudo", "mkdir", "-p", "/mnt/run/media/Second_Drive/BTCEcoandBackup/Bitcoin_Node"], buf)
@@ -1097,4 +1168,4 @@ class InstallerWindow(Adw.ApplicationWindow):
 
 if __name__ == "__main__":
     app = InstallerApp()
-    app.run(None)
\ No newline at end of file
+    app.run(None)
diff --git a/iso/sovran-install-headless.sh b/iso/sovran-install-headless.sh
index 440befe..bf9fc35 100755
--- a/iso/sovran-install-headless.sh
+++ b/iso/sovran-install-headless.sh
@@ -24,6 +24,7 @@ ROLE="server"
 DEPLOY_KEY=""
 HEADSCALE_SERVER=""
 HEADSCALE_KEY=""
+DATA_DISK_HAS_TIMECHAIN=false
 
 FLAKE="/etc/sovran/flake"
 LOG="/tmp/sovran-headless-install.log"
@@ -102,19 +103,42 @@ part_suffix() {
     fi
 }
 
+# ── Detect existing Bitcoin timechain data on data disk ───────────────────────
+if [[ -n "$DATA_DISK" ]]; then
+    DATA_P1=$(part_suffix "$DATA_DISK" 1)
+    if [[ -b "$DATA_P1" ]]; then
+        DATA_LABEL=$(lsblk -no LABEL "$DATA_P1" 2>/dev/null | head -n1 || true)
+        if [[ -z "$DATA_LABEL" ]]; then
+            DATA_LABEL=$(blkid -o value -s LABEL "$DATA_P1" 2>/dev/null || true)
+        fi
+
+        if [[ "$DATA_LABEL" == "BTCEcoandBackup" ]]; then
+            CHECK_MOUNT=$(mktemp -d /tmp/sovran-data-check.XXXXXX)
+            if mount -o ro "$DATA_P1" "$CHECK_MOUNT" 2>/dev/null; then
+                if [[ -d "$CHECK_MOUNT/BTCEcoandBackup/Bitcoin_Node" && -d "$CHECK_MOUNT/BTCEcoandBackup/Electrs_Data" ]]; then
+                    DATA_DISK_HAS_TIMECHAIN=true
+                    log "Existing Bitcoin timechain detected on data drive — preserving data"
+                fi
+                umount "$CHECK_MOUNT" || true
+            fi
+            rmdir "$CHECK_MOUNT" 2>/dev/null || true
+        fi
+    fi
+fi
+
 # ── Step 1: Wipe disks ────────────────────────────────────────────────────────
 log "=== Wiping disk(s) ==="
 
 sgdisk --zap-all "$DISK"
 wipefs --all --force "$DISK"
 
-if [[ -n "$DATA_DISK" ]]; then
+if [[ -n "$DATA_DISK" && "$DATA_DISK_HAS_TIMECHAIN" != true ]]; then
     sgdisk --zap-all "$DATA_DISK"
     wipefs --all --force "$DATA_DISK"
 fi
 
 partprobe "$DISK"
-[[ -n "$DATA_DISK" ]] && partprobe "$DATA_DISK"
+[[ -n "$DATA_DISK" && "$DATA_DISK_HAS_TIMECHAIN" != true ]] && partprobe "$DATA_DISK"
 sleep 2
 
 # ── Step 2: Partition OS disk ─────────────────────────────────────────────────
@@ -129,7 +153,7 @@ partprobe "$DISK"
 sleep 2
 
 # ── Step 3: Partition data disk (if present) ──────────────────────────────────
-if [[ -n "$DATA_DISK" ]]; then
+if [[ -n "$DATA_DISK" && "$DATA_DISK_HAS_TIMECHAIN" != true ]]; then
     log "=== Partitioning data disk ==="
     sgdisk \
         -n "1:1M:0" -t "1:8300" -c "1:primary" \
@@ -147,7 +171,7 @@ BOOT_P2=$(part_suffix "$DISK" 2)
 mkfs.vfat -F 32 "$BOOT_P1"
 mkfs.ext4 -F -L sovran_systemsos "$BOOT_P2"
 
-if [[ -n "$DATA_DISK" ]]; then
+if [[ -n "$DATA_DISK" && "$DATA_DISK_HAS_TIMECHAIN" != true ]]; then
     DATA_P1=$(part_suffix "$DATA_DISK" 1)
     mkfs.ext4 -F -L BTCEcoandBackup "$DATA_P1"
 fi