diff --git a/system/services/fat/fat.zig b/system/services/fat/fat.zig
index 8c405cc..fea3bc2 100644
--- a/system/services/fat/fat.zig
+++ b/system/services/fat/fat.zig
@@ -173,16 +173,23 @@ fn fatBringUp(endpoint: ipc.Handle) ?Harness.Volume {
     };
     std.log.info("mounted FAT ({s}, {d} clusters, partition lba {d})", .{ @tagName(filesystem.geometry.fat_type), filesystem.geometry.cluster_count, filesystem.base_lba });
 
-    // The volume mounts at its id-path (argv[2]), plus the two FHS rewrites so
-    // hierarchy paths (the logger's /system/logs) stay decoupled from which
-    // volume backs them. This single-volume increment's one volume IS the boot
-    // volume, so it installs both unconditionally; S3 (multi-volume) makes the
-    // rewrites content-conditional — installed only by whichever volume carries
-    // the system, decided by content, not order.
+    // Every volume mounts at its own id-path (argv[2]). The boot/system volume —
+    // the one carrying the /system tree — ADDITIONALLY installs the two FHS
+    // rewrites, so hierarchy paths (config reads, the logger's persistent
+    // /system/logs) stay decoupled from which volume backs them. Detection is by
+    // CONTENT, not spawn order: a volume is the system volume iff /system/
+    // configuration resolves on its own media. A data volume has no /system, so it
+    // mounts only at its id-path and never shadows the running system's config or
+    // logs with a dead mount.
     mount_specs[0] = .{ .prefix = volume_mount_prefix };
-    mount_specs[1] = .{ .prefix = "/system/configuration", .rewrite = "/system/configuration" };
-    mount_specs[2] = .{ .prefix = "/system/logs", .rewrite = "/system/logs" };
-    return .{ .engine = &filesystem, .mounts = mount_specs[0..3], .flush = flushIfDirty };
+    var mount_count: usize = 1;
+    if (filesystem.resolve("/system/configuration") != null) {
+        std.log.info("volume {d} carries the system tree; backing /system/configuration and /system/logs", .{my_volume_id});
+        mount_specs[1] = .{ .prefix = "/system/configuration", .rewrite = "/system/configuration" };
+        mount_specs[2] = .{ .prefix = "/system/logs", .rewrite = "/system/logs" };
+        mount_count = 3;
+    }
+    return .{ .engine = &filesystem, .mounts = mount_specs[0..mount_count], .flush = flushIfDirty };
 }
 
 pub fn main(init: process.Init) void {