diff --git a/DEBUG_INI.md b/DEBUG_INI.md
index fb297b9..ba91a46 100644
--- a/DEBUG_INI.md
+++ b/DEBUG_INI.md
@@ -45,6 +45,12 @@ Create the folder `sd:/config/omninx/` on the SD card if it does not exist. Same
 |-----|-----------------|
 | `skip_hekate_8gb_post_copy` | After a successful copy: the optional `hekate_8GB` / RAM menu and related file moves (see `install_hekate_8gb_post_copy` in `install.c`) |
 
+### Logging
+
+| Key | Effect |
+|-----|--------|
+| `log` | Writes `sd:/config/omninx/install.log` with every deleted path, every copied file and the final result. Nothing is skipped. Slower on large packs; meant for test runs. |
+
 ## Behaviour
 
 - On startup, if `debug.ini` exists and parses successfully, the payload prints a **DEBUG-MODUS** banner listing which skips are active.
diff --git a/Makefile b/Makefile
index 818e888..53245f0 100644
--- a/Makefile
+++ b/Makefile
@@ -60,7 +60,7 @@ OBJS_RAMTEST := $(filter-out $(BUILDDIR)/$(TARGET)/main.o,$(OBJS)) \
 all: $(OUTPUTDIR)/$(OUTPUT_NAME)
 	$(eval BIN_SIZE = $(shell wc -c < $(OUTPUTDIR)/$(OUTPUT_NAME)))
 	@echo "Payload size is $(BIN_SIZE) bytes (max $(MAX_PAYLOAD_SIZE) for RCM)"
-	@if [ $(BIN_SIZE) -gt $(MAX_PAYLOAD_SIZE) ]; then echo "WARNING: payload exceeds the RCM size limit"; fi
+	@if [ $(BIN_SIZE) -gt $(MAX_PAYLOAD_SIZE) ]; then echo "ERROR: payload exceeds the RCM size limit"; exit 1; fi
 
 clean:
 	@rm -rf $(BUILDDIR)
diff --git a/bdk/utils/sprintf.c b/bdk/utils/sprintf.c
index c53f15c..0a6389b 100644
--- a/bdk/utils/sprintf.c
+++ b/bdk/utils/sprintf.c
@@ -1,123 +1,128 @@
-/*
- * Copyright (c) 2019-2020 shchmue
- *
- * This program is free software; you can redistribute it and/or modify it
- * under the terms and conditions of the GNU General Public License,
- * version 2, as published by the Free Software Foundation.
- *
- * This program is distributed in the hope it will be useful, but WITHOUT
- * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
- * more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program.  If not, see <http://www.gnu.org/licenses/>.
- */
-
-#include "sprintf.h"
-
-#include <stdarg.h>
-
-static void _putc(char *buffer, const char c) {
-    *buffer = c;
-}
-
-static u32 _puts(char *buffer, const char *s) {
-    u32 count = 0;
-    for (; *s; s++, count++)
-        _putc(buffer + count, *s);
-    return count;
-}
-
-static u32 _putn(char *buffer, u32 v, int base, char fill, int fcnt) {
-    char buf[0x121];
-    static const char digits[] = "0123456789abcdefghijklmnopqrstuvwxyz";
-    char *p;
-    int c = fcnt;
-
-    if (base > 36)
-        return 0;
-
-    p = buf + 0x120;
-    *p = 0;
-    do {
-        c--;
-        *--p = digits[v % base];
-        v /= base;
-    } while (v);
-
-    if (fill != 0) {
-        while (c > 0) {
-            *--p = fill;
-            c--;
-        }
-    }
-
-    return _puts(buffer, p);
-}
-
-u32 s_printf(char *buffer, const char *fmt, ...) {
-    va_list ap;
-    int fill, fcnt;
-    u32 count = 0;
-
-    va_start(ap, fmt);
-    while(*fmt) {
-        if (*fmt == '%') {
-            fmt++;
-            fill = 0;
-            fcnt = 0;
-            if ((*fmt >= '0' && *fmt <= '9') || *fmt == ' ') {
-                fcnt = *fmt;
-                fmt++;
-                if (*fmt >= '0' && *fmt <= '9') {
-                    fill = fcnt;
-                    fcnt = *fmt - '0';
-                    fmt++;
-                } else {
-                    fill = ' ';
-                    fcnt -= '0';
-                }
-            }
-            switch (*fmt) {
-            case 'c':
-                _putc(buffer + count, va_arg(ap, u32));
-                count++;
-                break;
-            case 's':
-                count += _puts(buffer + count, va_arg(ap, char *));
-                break;
-            case 'd':
-                count += _putn(buffer + count, va_arg(ap, u32), 10, fill, fcnt);
-                break;
-            case 'p':
-            case 'P':
-            case 'x':
-            case 'X':
-                count += _putn(buffer + count, va_arg(ap, u32), 16, fill, fcnt);
-                break;
-            case '%':
-                _putc(buffer + count, '%');
-                count++;
-                break;
-            case '\0':
-                goto out;
-            default:
-                _putc(buffer + count, '%');
-                count++;
-                _putc(buffer + count, *fmt);
-                count++;
-                break;
-            }
-        } else {
-            _putc(buffer + count, *fmt);
-            count++;
-        }
-        fmt++;
-    }
-
-    out:
-    buffer[count] = 0;
-    va_end(ap);
-    return count;
+/*
+ * Copyright (c) 2019-2020 shchmue
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "sprintf.h"
+
+#include <stdarg.h>
+
+static void _putc(char *buffer, const char c) {
+    *buffer = c;
+}
+
+static u32 _puts(char *buffer, const char *s) {
+    u32 count = 0;
+    for (; *s; s++, count++)
+        _putc(buffer + count, *s);
+    return count;
+}
+
+static u32 _putn(char *buffer, u32 v, int base, char fill, int fcnt) {
+    char buf[0x121];
+    static const char digits[] = "0123456789abcdefghijklmnopqrstuvwxyz";
+    char *p;
+    int c = fcnt;
+
+    if (base > 36)
+        return 0;
+
+    p = buf + 0x120;
+    *p = 0;
+    do {
+        c--;
+        *--p = digits[v % base];
+        v /= base;
+    } while (v);
+
+    if (fill != 0) {
+        while (c > 0) {
+            *--p = fill;
+            c--;
+        }
+    }
+
+    return _puts(buffer, p);
+}
+
+u32 s_vprintf(char *buffer, const char *fmt, va_list ap) {
+    int fill, fcnt;
+    u32 count = 0;
+
+    while(*fmt) {
+        if (*fmt == '%') {
+            fmt++;
+            fill = 0;
+            fcnt = 0;
+            if ((*fmt >= '0' && *fmt <= '9') || *fmt == ' ') {
+                fcnt = *fmt;
+                fmt++;
+                if (*fmt >= '0' && *fmt <= '9') {
+                    fill = fcnt;
+                    fcnt = *fmt - '0';
+                    fmt++;
+                } else {
+                    fill = ' ';
+                    fcnt -= '0';
+                }
+            }
+            switch (*fmt) {
+            case 'c':
+                _putc(buffer + count, va_arg(ap, u32));
+                count++;
+                break;
+            case 's':
+                count += _puts(buffer + count, va_arg(ap, char *));
+                break;
+            case 'd':
+                count += _putn(buffer + count, va_arg(ap, u32), 10, fill, fcnt);
+                break;
+            case 'p':
+            case 'P':
+            case 'x':
+            case 'X':
+                count += _putn(buffer + count, va_arg(ap, u32), 16, fill, fcnt);
+                break;
+            case '%':
+                _putc(buffer + count, '%');
+                count++;
+                break;
+            case '\0':
+                goto out;
+            default:
+                _putc(buffer + count, '%');
+                count++;
+                _putc(buffer + count, *fmt);
+                count++;
+                break;
+            }
+        } else {
+            _putc(buffer + count, *fmt);
+            count++;
+        }
+        fmt++;
+    }
+
+    out:
+    buffer[count] = 0;
+    return count;
+}
+
+u32 s_printf(char *buffer, const char *fmt, ...) {
+    va_list ap;
+    va_start(ap, fmt);
+    u32 count = s_vprintf(buffer, fmt, ap);
+    va_end(ap);
+    return count;
 }
\ No newline at end of file
diff --git a/bdk/utils/sprintf.h b/bdk/utils/sprintf.h
index 0737775..7e2ef57 100644
--- a/bdk/utils/sprintf.h
+++ b/bdk/utils/sprintf.h
@@ -1,24 +1,26 @@
-/*
- * Copyright (c) 2019-2020 shchmue
- *
- * This program is free software; you can redistribute it and/or modify it
- * under the terms and conditions of the GNU General Public License,
- * version 2, as published by the Free Software Foundation.
- *
- * This program is distributed in the hope it will be useful, but WITHOUT
- * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
- * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
- * more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program.  If not, see <http://www.gnu.org/licenses/>.
- */
-
-#ifndef _SPRINTF_H_
-#define _SPRINTF_H_
-
-#include "types.h"
-
-u32 s_printf(char *buffer, const char *fmt, ...);
-
-#endif
+/*
+ * Copyright (c) 2019-2020 shchmue
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef _SPRINTF_H_
+#define _SPRINTF_H_
+
+#include "types.h"
+#include <stdarg.h>
+
+u32 s_printf(char *buffer, const char *fmt, ...);
+u32 s_vprintf(char *buffer, const char *fmt, va_list ap);
+
+#endif
diff --git a/source/fs.c b/source/fs.c
index 62053b5..7002a34 100644
--- a/source/fs.c
+++ b/source/fs.c
@@ -9,14 +9,15 @@
 #include <string.h>
 #include <utils/sprintf.h>
 #include <stdarg.h>
-#include <stdio.h>
 
 #define FS_BUFFER_SIZE 0x100000  // 1MB copy buffer
-#define LOG_BUFFER_SIZE 512
+#define LOG_BUFFER_SIZE 1024 // fits two 255-char paths plus text
+#define LOG_SYNC_EVERY  16
 
 // Log file handle
 static FIL log_file;
 static bool log_enabled = false;
+static u32 log_lines;
 static char log_buf[LOG_BUFFER_SIZE];
 
 // Initialize log file
@@ -24,6 +25,7 @@ void log_init(const char *path) {
     int res = f_open(&log_file, path, FA_WRITE | FA_CREATE_ALWAYS);
     if (res == FR_OK) {
         log_enabled = true;
+        log_lines = 0;
         log_write("=== OmniNX Installer Log ===\n\n");
     }
 }
@@ -44,15 +46,19 @@ void log_write(const char *fmt, ...) {
     va_list args;
     va_start(args, fmt);
 
-    // Format the message
-    vsnprintf(log_buf, LOG_BUFFER_SIZE, fmt, args);
+    // BDK formatter (no newlib printf). Callers keep paths <= 255 chars.
+    u32 len = s_vprintf(log_buf, fmt, args);
 
     va_end(args);
 
-    // Write to file
     UINT bw;
-    f_write(&log_file, log_buf, strlen(log_buf), &bw);
-    f_sync(&log_file);  // Flush to ensure data is written
+    f_write(&log_file, log_buf, len, &bw);
+    if (++log_lines % LOG_SYNC_EVERY == 0)
+        f_sync(&log_file);
+}
+
+bool log_is_enabled(void) {
+    return log_enabled;
 }
 
 // Convert FatFS error code to string
diff --git a/source/fs.h b/source/fs.h
index 9af9e22..2fb1309 100644
--- a/source/fs.h
+++ b/source/fs.h
@@ -18,3 +18,4 @@ int folder_delete(const char *path);
 void log_init(const char *path);
 void log_close(void);
 void log_write(const char *fmt, ...);
+bool log_is_enabled(void);
diff --git a/source/install.c b/source/install.c
index e649c74..8dec1b9 100644
--- a/source/install.c
+++ b/source/install.c
@@ -289,7 +289,9 @@ int folder_copy_with_progress_v2(const char *src, const char *dst, const char *d
     install_set_color(COLOR_WHITE);
     
     // Perform the copy with progress updates
+    log_write("COPY TREE %s -> %s (%d Eintraege)\n", src, dst, (u32)total);
     res = folder_copy_progress_recursive(src, dst, &copied, total, start_x, start_y, display_name, &last_percent);
+    log_write("COPY TREE %s: %s\n", src, fs_error_str(res));
     
     // Final update - overwrite the same line
     gfx_con_setpos(start_x, start_y);
@@ -499,6 +501,7 @@ int delete_path_lists_grouped(const char *folder_display_name, ...) {
             res = f_unlink(path);
         }
 
+        log_write("DELETE %s: %s\n", path, fs_error_str(res));
         if (res == FR_OK || res == FR_NO_FILE)
             deleted++;
         else
@@ -1343,6 +1346,7 @@ static void install_extras_post_copy(void)
 }
 
 #define INSTALL_DEBUG_INI "sd:/config/omninx/debug.ini"
+#define INSTALL_LOG_PATH  "sd:/config/omninx/install.log"
 
 typedef struct {
     bool active;
@@ -1356,6 +1360,7 @@ typedef struct {
     bool skip_update_staging_cleanup;
     bool skip_update_horizon_oc;
     bool skip_hekate_8gb_post_copy;
+    bool log;
 } install_debug_opts_t;
 
 static void install_debug_load(install_debug_opts_t *d)
@@ -1397,6 +1402,8 @@ static void install_debug_load(install_debug_opts_t *d)
                 d->skip_update_horizon_oc = install_ini_kv_truth(kv->val);
             else if (strcmp(kv->key, "skip_hekate_8gb_post_copy") == 0)
                 d->skip_hekate_8gb_post_copy = install_ini_kv_truth(kv->val);
+            else if (strcmp(kv->key, "log") == 0)
+                d->log = install_ini_kv_truth(kv->val);
         }
         break;
     }
@@ -1405,7 +1412,7 @@ static void install_debug_load(install_debug_opts_t *d)
     d->active = d->skip_clean_backup || d->skip_clean_wipe || d->skip_clean_restore
         || d->skip_clean_install || d->skip_clean_staging_cleanup || d->skip_update_cleanup
         || d->skip_update_install || d->skip_update_staging_cleanup || d->skip_update_horizon_oc
-        || d->skip_hekate_8gb_post_copy;
+        || d->skip_hekate_8gb_post_copy || d->log;
 }
 
 static void install_debug_print_banner(const install_debug_opts_t *d)
@@ -1435,17 +1442,39 @@ static void install_debug_print_banner(const install_debug_opts_t *d)
         gfx_printf("  ueberspringe: HorizonOC Update (Backup/Restore)\n");
     if (d->skip_hekate_8gb_post_copy)
         gfx_printf("  ueberspringe: extras RAM / Hekate-Auswahl / Post-Copy\n");
+    if (d->log)
+        gfx_printf("  Log: %s\n", INSTALL_LOG_PATH);
     install_set_color(COLOR_WHITE);
     gfx_printf("\n");
 }
 
+static int perform_installation_steps(omninx_variant_t pack_variant, install_mode_t mode, const install_debug_opts_t *d);
+
 // Main installation function
 int perform_installation(omninx_variant_t pack_variant, install_mode_t mode) {
-    int res;
     install_debug_opts_t dbg;
     install_debug_load(&dbg);
     install_debug_print_banner(&dbg);
 
+    if (dbg.log) {
+        log_init(INSTALL_LOG_PATH);
+        log_write("Version: %s\nModus: %s\nVariante: %d\n\n", VERSION,
+            mode == INSTALL_MODE_UPDATE ? "Update" : "Clean", (u32)pack_variant);
+    }
+
+    int res = perform_installation_steps(pack_variant, mode, &dbg);
+
+    if (log_is_enabled()) {
+        log_write("\n=== Ende: res=%d (%s) ===\n", (u32)res, fs_error_str(res));
+        log_close();
+    }
+    return res;
+}
+
+static int perform_installation_steps(omninx_variant_t pack_variant, install_mode_t mode, const install_debug_opts_t *d) {
+    int res;
+    const install_debug_opts_t dbg = *d;
+
     if (mode == INSTALL_MODE_UPDATE) {
         if (pack_variant == VARIANT_OC && !dbg.skip_update_horizon_oc) {
             bool had_horizon_cfg = install_path_exists(HORIZON_OC_CONFIG_PATH);