diff --git a/Source/Core/Common/CMakeLists.txt b/Source/Core/Common/CMakeLists.txt
index 1edb201350..86fd37a788 100644
--- a/Source/Core/Common/CMakeLists.txt
+++ b/Source/Core/Common/CMakeLists.txt
@@ -45,6 +45,7 @@ add_library(common
   EnumMap.h
   Event.h
   FatFsUtil.cpp
+  FatFsUtil.h
   FileSearch.cpp
   FileSearch.h
   FileUtil.cpp
diff --git a/Source/Core/Common/FatFsUtil.cpp b/Source/Core/Common/FatFsUtil.cpp
index 4d8b450529..ffd42e68ab 100644
--- a/Source/Core/Common/FatFsUtil.cpp
+++ b/Source/Core/Common/FatFsUtil.cpp
@@ -1,8 +1,14 @@
 // Copyright 2022 Dolphin Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
+#include "Common/FatFsUtil.h"
+
+#include <algorithm>
+#include <cmath>
 #include <cstdlib>
 #include <mutex>
+#include <string>
+#include <vector>
 
 // Does not compile if diskio.h is included first.
 // clang-format off
@@ -10,36 +16,102 @@
 #include "diskio.h"
 // clang-format on
 
-// For now this is just mostly dummy functions so FatFs actually links.
+#include "Common/Align.h"
+#include "Common/FileUtil.h"
+#include "Common/IOFile.h"
+#include "Common/Logging/Log.h"
+#include "Common/StringUtil.h"
+
+enum : u32
+{
+  SECTOR_SIZE = 512,
+  MAX_CLUSTER_SIZE = 64 * SECTOR_SIZE,
+};
+
+static std::mutex s_fatfs_mutex;
+static File::IOFile s_image;
 
 extern "C" DSTATUS disk_status(BYTE pdrv)
 {
-  return STA_NOINIT;
+  return 0;
 }
 
 extern "C" DSTATUS disk_initialize(BYTE pdrv)
 {
-  return STA_NOINIT;
+  return 0;
 }
 
 extern "C" DRESULT disk_read(BYTE pdrv, BYTE* buff, LBA_t sector, UINT count)
 {
-  return RES_PARERR;
+  const u64 offset = static_cast<u64>(sector) * SECTOR_SIZE;
+  if (!s_image.Seek(offset, File::SeekOrigin::Begin))
+  {
+    ERROR_LOG_FMT(COMMON, "SD image seek failed (offset={})", offset);
+    return RES_ERROR;
+  }
+
+  const size_t size = static_cast<size_t>(count) * SECTOR_SIZE;
+  if (!s_image.ReadBytes(buff, size))
+  {
+    ERROR_LOG_FMT(COMMON, "SD image read failed (offset={}, size={})", offset, size);
+    return RES_ERROR;
+  }
+
+  return RES_OK;
 }
 
 extern "C" DRESULT disk_write(BYTE pdrv, const BYTE* buff, LBA_t sector, UINT count)
 {
-  return RES_PARERR;
+  const u64 offset = static_cast<u64>(sector) * SECTOR_SIZE;
+  if (!s_image.Seek(offset, File::SeekOrigin::Begin))
+  {
+    ERROR_LOG_FMT(COMMON, "SD image seek failed (offset={})", offset);
+    return RES_ERROR;
+  }
+
+  const size_t size = static_cast<size_t>(count) * SECTOR_SIZE;
+  if (!s_image.WriteBytes(buff, size))
+  {
+    ERROR_LOG_FMT(COMMON, "SD image write failed (offset={}, size={})", offset, size);
+    return RES_ERROR;
+  }
+
+  return RES_OK;
 }
 
 extern "C" DRESULT disk_ioctl(BYTE pdrv, BYTE cmd, void* buff)
 {
-  return RES_PARERR;
+  switch (cmd)
+  {
+  case CTRL_SYNC:
+    return RES_OK;
+  case GET_SECTOR_COUNT:
+    *reinterpret_cast<LBA_t*>(buff) = s_image.GetSize() / SECTOR_SIZE;
+    return RES_OK;
+  default:
+    WARN_LOG_FMT(COMMON, "Unexpected SD image ioctl {}", cmd);
+    return RES_OK;
+  }
 }
 
 extern "C" DWORD get_fattime(void)
 {
-  return 0;
+  const std::time_t time = std::time(nullptr);
+  std::tm tm;
+#ifdef _WIN32
+  localtime_s(&tm, &time);
+#else
+  localtime_r(&time, &tm);
+#endif
+
+  DWORD fattime = 0;
+  fattime |= (tm.tm_year - 80) << 25;
+  fattime |= (tm.tm_mon + 1) << 21;
+  fattime |= tm.tm_mday << 16;
+  fattime |= tm.tm_hour << 11;
+  fattime |= tm.tm_min << 5;
+  fattime |= std::min(tm.tm_sec, 59) >> 1;
+  return fattime;
 }
 
 extern "C" void* ff_memalloc(UINT msize)
@@ -76,3 +148,344 @@ extern "C" int ff_del_syncobj(FF_SYNC_t sobj)
   delete reinterpret_cast<std::recursive_mutex*>(sobj);
   return 1;
 }
+
+namespace Common
+{
+static constexpr u64 MebibytesToBytes(u64 mebibytes)
+{
+  return mebibytes * 1024 * 1024;
+}
+
+static constexpr u64 GibibytesToBytes(u64 gibibytes)
+{
+  return gibibytes * 1024 * 1024 * 1024;
+}
+
+static bool CheckIfFATCompatible(const File::FSTEntry& entry)
+{
+  if (!entry.isDirectory)
+    return true;
+
+  if (entry.children.size() > 65536)
+  {
+    ERROR_LOG_FMT(COMMON, "Directory {} has too many entries ({})", entry.physicalName,
+                  entry.children.size());
+    return false;
+  }
+
+  for (const File::FSTEntry& child : entry.children)
+  {
+    const size_t size = UTF8ToUTF16(child.virtualName).size();
+    if (size > 255)
+    {
+      ERROR_LOG_FMT(COMMON, "Filename {0} (in directory {1}) is too long ({2})", child.virtualName,
+                    entry.physicalName, size);
+      return false;
+    }
+
+    if (child.size >= GibibytesToBytes(4))
+    {
+      ERROR_LOG_FMT(COMMON, "File {0} (in directory {1}) is too large ({2})", child.virtualName,
+                    entry.physicalName, child.size);
+      return false;
+    }
+
+    if (!CheckIfFATCompatible(child))
+      return false;
+  }
+
+  return true;
+}
+
+static u64 GetSize(const File::FSTEntry& entry)
+{
+  if (!entry.isDirectory)
+    return AlignUp(entry.size, MAX_CLUSTER_SIZE);
+
+  u64 size = 0;
+  for (const File::FSTEntry& child : entry.children)
+  {
+    size += 32;
+    // For simplicity, assume that all names are LFN.
+    const u64 num_lfn_entries = (UTF8ToUTF16(child.virtualName).size() + 13 - 1) / 13;
+    size += num_lfn_entries * 32;
+  }
+  size = AlignUp(size, MAX_CLUSTER_SIZE);
+
+  for (const File::FSTEntry& child : entry.children)
+    size += GetSize(child);
+
+  return size;
+}
+
+static bool Pack(const File::FSTEntry& entry, bool is_root, std::vector<u8>& tmp_buffer)
+{
+  if (!entry.isDirectory)
+  {
+    File::IOFile src(entry.physicalName, "rb");
+    if (!src)
+      return false;
+
+    FIL dst;
+    if (f_open(&dst, entry.virtualName.c_str(), FA_CREATE_ALWAYS | FA_WRITE) != FR_OK)
+      return false;
+
+    if (src.GetSize() != entry.size)
+      return false;
+
+    if (entry.size >= GibibytesToBytes(4))
+      return false;
+
+    u64 size = entry.size;
+    while (size > 0)
+    {
+      u32 chunk_size = static_cast<u32>(std::min(size, static_cast<u64>(tmp_buffer.size())));
+      if (!src.ReadBytes(tmp_buffer.data(), chunk_size))
+        return false;
+
+      u32 written_size;
+      if (f_write(&dst, tmp_buffer.data(), chunk_size, &written_size) != FR_OK)
+        return false;
+
+      if (written_size != chunk_size)
+        return false;
+
+      size -= chunk_size;
+    }
+
+    if (f_close(&dst) != FR_OK)
+      return false;
+
+    if (!src.Close())
+      return false;
+
+    return true;
+  }
+
+  if (!is_root)
+  {
+    if (f_mkdir(entry.virtualName.c_str()) != FR_OK)
+      return false;
+
+    if (f_chdir(entry.virtualName.c_str()) != FR_OK)
+      return false;
+  }
+
+  for (const File::FSTEntry& child : entry.children)
+  {
+    if (!Pack(child, false, tmp_buffer))
+      return false;
+  }
+
+  if (!is_root)
+  {
+    if (f_chdir("..") != FR_OK)
+      return false;
+  }
+
+  return true;
+}
+
+bool SyncSDFolderToSDImage()
+{
+  const std::string root_path = File::GetUserPath(D_WIISDCARDSYNCFOLDER_IDX);
+  if (!File::IsDirectory(root_path))
+    return false;
+
+  const File::FSTEntry root = File::ScanDirectoryTree(root_path, true);
+  if (!CheckIfFATCompatible(root))
+    return false;
+
+  u64 size = GetSize(root);
+  // Allocate a reasonable amount of free space
+  size += std::clamp(size / 2, MebibytesToBytes(512), GibibytesToBytes(8));
+  size = AlignUp(size, MAX_CLUSTER_SIZE);
+
+  std::lock_guard lk(s_fatfs_mutex);
+
+  const std::string image_path = File::GetUserPath(F_WIISDCARDIMAGE_IDX);
+  const std::string temp_image_path = File::GetTempFilenameForAtomicWrite(image_path);
+  if (!s_image.Open(temp_image_path, "w+b"))
+  {
+    ERROR_LOG_FMT(COMMON, "Failed to open SD image");
+    return false;
+  }
+
+  if (!s_image.Resize(size))
+  {
+    ERROR_LOG_FMT(COMMON, "Failed to allocate space for SD image");
+    s_image.Close();
+    File::Delete(temp_image_path);
+    return false;
+  }
+
+  MKFS_PARM options = {};
+  options.fmt = FM_FAT32;
+  options.n_fat = 0;    // Number of FATs: automatic
+  options.align = 1;    // Alignment of the data region (in sectors)
+  options.n_root = 0;   // Number of root directory entries: automatic (and unused for FAT32)
+  options.au_size = 0;  // Cluster size: automatic
+
+  std::vector<u8> tmp_buffer(MAX_CLUSTER_SIZE);
+  if (f_mkfs("", &options, tmp_buffer.data(), static_cast<UINT>(tmp_buffer.size())) != FR_OK)
+  {
+    ERROR_LOG_FMT(COMMON, "Failed to initialize SD image filesystem");
+    s_image.Close();
+    File::Delete(temp_image_path);
+    return false;
+  }
+
+  FATFS fs;
+  f_mount(&fs, "", 0);
+
+  if (!Pack(root, true, tmp_buffer))
+  {
+    ERROR_LOG_FMT(COMMON, "Failed to pack SD image");
+    s_image.Close();
+    File::Delete(temp_image_path);
+    return false;
+  }
+
+  f_unmount("");
+
+  if (!s_image.Close())
+  {
+    ERROR_LOG_FMT(COMMON, "Failed to close SD image");
+    return false;
+  }
+  if (!File::Rename(temp_image_path, image_path))
+  {
+    ERROR_LOG_FMT(COMMON, "Failed to rename SD image");
+    return false;
+  }
+
+  INFO_LOG_FMT(COMMON, "Successfully packed SD image");
+  return true;
+}
+
+static bool Unpack(const std::string path, bool is_directory, const char* name,
+                   std::vector<u8>& tmp_buffer)
+{
+  if (!is_directory)
+  {
+    FIL src;
+    if (f_open(&src, name, FA_READ) != FR_OK)
+      return false;
+
+    File::IOFile dst(path, "wb");
+    if (!dst)
+      return false;
+
+    u32 size = f_size(&src);
+    while (size > 0)
+    {
+      u32 chunk_size = std::min(size, static_cast<u32>(tmp_buffer.size()));
+      u32 read_size;
+      if (f_read(&src, tmp_buffer.data(), chunk_size, &read_size) != FR_OK)
+        return false;
+
+      if (read_size != chunk_size)
+        return false;
+
+      if (!dst.WriteBytes(tmp_buffer.data(), chunk_size))
+        return false;
+
+      size -= chunk_size;
+    }
+
+    if (!dst.Close())
+      return false;
+
+    if (f_close(&src) != FR_OK)
+      return false;
+
+    return true;
+  }
+
+  if (!File::CreateDir(path))
+    return false;
+
+  if (f_chdir(name) != FR_OK)
+    return false;
+
+  DIR directory;
+  if (f_opendir(&directory, ".") != FR_OK)
+    return false;
+
+  FILINFO entry;
+  while (true)
+  {
+    if (f_readdir(&directory, &entry) != FR_OK)
+      return false;
+
+    if (entry.fname[0] == '\0')
+      break;
+
+    if (!Unpack(path + "/" + entry.fname, entry.fattrib & AM_DIR, entry.fname, tmp_buffer))
+      return false;
+  }
+
+  if (f_closedir(&directory) != FR_OK)
+    return false;
+
+  if (f_chdir("..") != FR_OK)
+    return false;
+
+  return true;
+}
+
+bool SyncSDImageToSDFolder()
+{
+  const std::string image_path = File::GetUserPath(F_WIISDCARDIMAGE_IDX);
+
+  std::lock_guard lk(s_fatfs_mutex);
+  if (!s_image.Open(image_path, "r+b"))
+  {
+    ERROR_LOG_FMT(COMMON, "Failed to open SD image");
+    return false;
+  }
+
+  FATFS fs;
+  f_mount(&fs, "", 0);
+
+  // Most systems don't offer atomic directory renaming, so it's simpler to directly work on the
+  // actual one and rollback if needed.
+  const std::string root_path = File::GetUserPath(D_WIISDCARDSYNCFOLDER_IDX);
+  if (root_path.empty())
+    return false;
+
+  // Unpack() and GetTempFilenameForAtomicWrite() don't want the trailing separator.
+  const std::string target_dir = root_path.substr(0, root_path.length() - 1);
+
+  File::CreateDir(root_path);
+  const std::string temp_root_path = File::GetTempFilenameForAtomicWrite(target_dir);
+  if (!File::Rename(target_dir, temp_root_path))
+  {
+    ERROR_LOG_FMT(COMMON, "Failed to backup SD folder");
+    return false;
+  }
+
+  std::vector<u8> tmp_buffer(MAX_CLUSTER_SIZE);
+  if (!Unpack(target_dir, true, "", tmp_buffer))
+  {
+    ERROR_LOG_FMT(COMMON, "Failed to unpack SD image");
+    File::DeleteDirRecursively(target_dir);
+    File::Rename(temp_root_path, target_dir);
+    return false;
+  }
+
+  f_unmount("");
+
+  if (!s_image.Close())
+  {
+    ERROR_LOG_FMT(COMMON, "Failed to close SD image");
+    File::DeleteDirRecursively(target_dir);
+    File::Rename(temp_root_path, target_dir);
+    return false;
+  }
+
+  File::DeleteDirRecursively(temp_root_path);
+  INFO_LOG_FMT(COMMON, "Successfully unpacked SD image");
+  return true;
+}
+}  // namespace Common
diff --git a/Source/Core/Common/FatFsUtil.h b/Source/Core/Common/FatFsUtil.h
new file mode 100644
index 0000000000..bb981e2267
--- /dev/null
+++ b/Source/Core/Common/FatFsUtil.h
@@ -0,0 +1,12 @@
+// Copyright 2022 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include "Common/CommonTypes.h"
+
+namespace Common
+{
+bool SyncSDFolderToSDImage();
+bool SyncSDImageToSDFolder();
+}  // namespace Common
diff --git a/Source/Core/Core/Core.cpp b/Source/Core/Core/Core.cpp
index 56c1342050..79ac6a2ae6 100644
--- a/Source/Core/Core/Core.cpp
+++ b/Source/Core/Core/Core.cpp
@@ -25,6 +25,7 @@
 #include "Common/CommonTypes.h"
 #include "Common/Event.h"
 #include "Common/FPURoundMode.h"
+#include "Common/FatFsUtil.h"
 #include "Common/FileUtil.h"
 #include "Common/Flag.h"
 #include "Common/Logging/Log.h"
@@ -495,6 +496,16 @@ static void EmuThread(std::unique_ptr<BootParameters> boot, WindowSystemInfo wsi
   const bool delete_savestate =
       boot_session_data.GetDeleteSavestate() == DeleteSavestateAfterBoot::Yes;
 
+  bool sync_sd_folder = core_parameter.bWii && Config::Get(Config::MAIN_WII_SD_CARD) &&
+                        Config::Get(Config::MAIN_WII_SD_CARD_ENABLE_FOLDER_SYNC);
+  if (sync_sd_folder)
+    sync_sd_folder = Common::SyncSDFolderToSDImage();
+
+  Common::ScopeGuard sd_folder_sync_guard{[sync_sd_folder] {
+    if (sync_sd_folder && Config::Get(Config::MAIN_ALLOW_SD_WRITES))
+      Common::SyncSDImageToSDFolder();
+  }};
+
   // Load and Init Wiimotes - only if we are booting in Wii mode
   bool init_wiimotes = false;
   if (core_parameter.bWii && !Config::Get(Config::MAIN_BLUETOOTH_PASSTHROUGH_ENABLED))
diff --git a/Source/Core/DolphinLib.props b/Source/Core/DolphinLib.props
index 17c2aa4345..13d1525b74 100644
--- a/Source/Core/DolphinLib.props
+++ b/Source/Core/DolphinLib.props
@@ -45,6 +45,7 @@
     <ClInclude Include="Common\EnumFormatter.h" />
     <ClInclude Include="Common\EnumMap.h" />
     <ClInclude Include="Common\Event.h" />
+    <ClInclude Include="Common\FatFsUtil.h" />
     <ClInclude Include="Common\FileSearch.h" />
     <ClInclude Include="Common\FileUtil.h" />
     <ClInclude Include="Common\FixedSizeQueue.h" />