Refs相对Ntfs来说，有一个很重要的技术 Block Clone。
块克隆指令文件系统代表应用程序复制一段文件字节，目标文件可能与源文件相同，也可能不同。不幸的是，传统的复制操作成本高昂，因为它们会触发对底层物理数据的昂贵读写操作。
然而，在ReFS中，块克隆执行的是低成本元数据操作，而不是读取和写入文件数据。因为ReFS允许多个文件共享相同的逻辑簇（卷上的物理位置），复制操作只需将文件的一个区域重新映射到单独的物理位置，将昂贵的物理操作转换为快速的逻辑操作。这使得复制操作能够更快完成，并且对底层存储的I/O操作更少。这项改进也惠及了虚拟化工作负载，因为在使用块克隆操作时，.vhdx检查点合并操作的速度显著提升。此外，由于多个文件可以共享相同的逻辑簇，相同的数据不会多次物理存储，从而提高了存储容量。
根据MS DOCS所述，Block Clone允许多个文件共享一个物理区块，减少文件复制时候占用额外的资源。因此我们可以借助这个技术来实现类似BtrFS的COW(Copy On Write)技术。
FILE_SUPPORTS_BLOCK_REFCOUNTING 可以判断文件是否支持Block Clone。
参考代码：
实现代码
#include <atlbase.h>#include <windows.h>#include <winioctl.h>#include <crtdbg.h>#include <CLocale>constexpr LONG64 inline ROUNDUP(LONG64 file_size, ULONG cluster_size) noexcept{ return (file_size + cluster_size - 1) / cluster_size * cluster_size;}BOOL CreateForkW(HANDLE hSrc, HANDLE hDst){ DWORD fs_flags; if (!GetVolumeInformationByHandleW(hSrc, NULL, 0, NULL, NULL, &fs_flags, NULL, 0)) { return FALSE; } if (!(fs_flags & FILE_SUPPORTS_BLOCK_REFCOUNTING)) { SetLastError(ERROR_NOT_CAPABLE); return FALSE; } FILE_END_OF_FILE_INFO file_size; if (!GetFileSizeEx(hSrc, &file_size.EndOfFile)) { return FALSE; } FILE_BASIC_INFO file_basic; if (!GetFileInformationByHandleEx(hSrc, FileBasicInfo, &file_basic, sizeof file_basic)) { return FALSE; } DWORD _; FSCTL_GET_INTEGRITY_INFORMATION_BUFFER get_integrity; if (!DeviceIoControl(hSrc, FSCTL_GET_INTEGRITY_INFORMATION, nullptr, 0, &get_integrity, sizeof get_integrity, &_, nullptr)) { return FALSE; } FILE_DISPOSITION_INFO dispos = { TRUE }; if (!SetFileInformationByHandle(hDst, FileDispositionInfo, &dispos, sizeof dispos)) { return FALSE; } if (!DeviceIoControl(hDst, FSCTL_SET_SPARSE, NULL, 0, NULL, 0, &_, NULL)) { return FALSE; } FSCTL_SET_INTEGRITY_INFORMATION_BUFFER set_integrity = { get_integrity.ChecksumAlgorithm, get_integrity.Reserved, get_integrity.Flags }; if (!DeviceIoControl(hDst, FSCTL_SET_INTEGRITY_INFORMATION, &set_integrity, sizeof set_integrity, nullptr, 0, nullptr, nullptr)) { return FALSE; } if (!SetFileInformationByHandle(hDst, FileEndOfFileInfo, &file_size, sizeof file_size)) { return FALSE; } const LONG64 split_threshold = (1LL << 32) - get_integrity.ClusterSizeInBytes; DUPLICATE_EXTENTS_DATA dup_extent; dup_extent.FileHandle = hSrc; for (LONG64 offset = 0, remain = ROUNDUP(file_size.EndOfFile.QuadPart, get_integrity.ClusterSizeInBytes); remain > 0; offset += split_threshold, remain -= split_threshold) { dup_extent.SourceFileOffset.QuadPart = dup_extent.TargetFileOffset.QuadPart = offset; dup_extent.ByteCount.QuadPart = min(split_threshold, remain); _ASSERTE(dup_extent.SourceFileOffset.QuadPart % get_integrity.ClusterSizeInBytes == 0); _ASSERTE(dup_extent.ByteCount.QuadPart % get_integrity.ClusterSizeInBytes == 0); _ASSERTE(dup_extent.ByteCount.QuadPart <= UINT32_MAX); _RPT3(_CRT_WARN, "Remain=%llx\nOffset=%llx\nLength=%llx\n\n", remain, dup_extent.SourceFileOffset.QuadPart, dup_extent.ByteCount.QuadPart); if (!DeviceIoControl(hDst, FSCTL_DUPLICATE_EXTENTS_TO_FILE, &dup_extent, sizeof dup_extent, nullptr, 0, &_, nullptr)) { _CrtDbgBreak(); return FALSE; } } if (!(file_basic.FileAttributes & FILE_ATTRIBUTE_SPARSE_FILE)) { FILE_SET_SPARSE_BUFFER set_sparse = { FALSE }; if (!DeviceIoControl(hDst, FSCTL_SET_SPARSE, &set_sparse, sizeof set_sparse, nullptr, 0, &_, nullptr)) { return FALSE; } } file_basic.CreationTime.QuadPart = 0; if (!SetFileInformationByHandle(hDst, FileBasicInfo, &file_basic, sizeof file_basic)) { return FALSE; } if (!FlushFileBuffers(hDst)) { return FALSE; } dispos = { FALSE }; return !!SetFileInformationByHandle(hDst, FileDispositionInfo, &dispos, sizeof dispos);}BOOL CreateForkForFileW(LPCWSTR SrcFile, LPCWSTR DstFile){#ifdef DEBUG _putws(SrcFile);#endif // DEBUG // Judge both files are in the same volume WCHAR src_volume[MAX_PATH], dst_volume[MAX_PATH]; if (GetVolumePathNameW(SrcFile, src_volume, MAX_PATH) == 0 || GetVolumePathNameW(DstFile, dst_volume, MAX_PATH) == 0) { return FALSE; } if (lstrcmpiW(src_volume, dst_volume) != 0) { SetLastError(ERROR_NOT_SAME_DEVICE); return FALSE; } HANDLE hSrc = CreateFileW(SrcFile, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, 0, NULL); if (hSrc == INVALID_HANDLE_VALUE) { CloseHandle(hSrc); return FALSE; } HANDLE hDst = CreateFileW(DstFile, GENERIC_READ | GENERIC_WRITE | DELETE, 0, nullptr, CREATE_NEW, 0, hSrc); if (hDst == INVALID_HANDLE_VALUE) { SetLastError(ERROR_FILE_EXISTS); CloseHandle(hDst); CloseHandle(hSrc); return FALSE; } BOOL ret = CreateForkW(hSrc, hDst); CloseHandle(hDst); CloseHandle(hSrc); return ret;}BOOL CreateForkForDirW(LPCWSTR SrcDir, LPCWSTR DstDir){ // Judge SrcDir is a directory DWORD attr = GetFileAttributesW(SrcDir); if (attr == INVALID_FILE_ATTRIBUTES || !(attr & FILE_ATTRIBUTE_DIRECTORY)) { return FALSE; } // Judge both directories are in the same volume WCHAR src_volume[MAX_PATH], dst_volume[MAX_PATH]; if (GetVolumePathNameW(SrcDir, src_volume, MAX_PATH) == 0 || GetVolumePathNameW(DstDir, dst_volume, MAX_PATH) == 0) { return FALSE; } if (lstrcmpiW(src_volume, dst_volume) != 0) { SetLastError(ERROR_NOT_SAME_DEVICE); return FALSE; } HANDLE hSrc = CreateFileW(SrcDir, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL); if (hSrc == INVALID_HANDLE_VALUE) { CloseHandle(hSrc); return FALSE; } DWORD fs_flags; if (!GetVolumeInformationByHandleW(hSrc, NULL, 0, NULL, NULL, &fs_flags, NULL, 0)) { return FALSE; } if (!(fs_flags & FILE_SUPPORTS_BLOCK_REFCOUNTING)) { SetLastError(ERROR_NOT_CAPABLE); return FALSE; } CloseHandle(hSrc); if (!CreateDirectoryW(DstDir, NULL)) { return FALSE; } // Enumerate all files in the directory WCHAR src_dir[MAX_PATH]; lstrcpyW(src_dir, SrcDir); PathAppendW(src_dir, L"*"); WIN32_FIND_DATAW find_data; HANDLE hFind = FindFirstFileW(src_dir, &find_data); if (hFind == INVALID_HANDLE_VALUE) { return FALSE; } do { // ignore current and father path if (StrCmpW(find_data.cFileName, L".") == 0 || StrCmpW(find_data.cFileName, L"..") == 0) continue; // if it is a directory, create a new directory. And then recursively call this function. if (find_data.dwFileAttributes & FILE_ATTRIBUTE_DIRECTORY) { WCHAR src_subdir[MAX_PATH], dst_subdir[MAX_PATH]; StrCpyW(src_subdir, SrcDir); StrCpyW(dst_subdir, DstDir); PathAppendW(src_subdir, find_data.cFileName); PathAppendW(dst_subdir, find_data.cFileName); if (!CreateForkForDirW(src_subdir, dst_subdir)) { FindClose(hFind); return FALSE; } } else { WCHAR src_file[MAX_PATH], dst_file[MAX_PATH]; StrCpyW(src_file, SrcDir); StrCpyW(dst_file, DstDir); PathAppendW(src_file, find_data.cFileName); PathAppendW(dst_file, find_data.cFileName); if (!CreateForkForFileW(src_file, dst_file)) { CloseHandle(hFind); return FALSE; } } } while (FindNextFile(hFind, &find_data) != 0); return TRUE;}int main(){ setlocale(LC_ALL, "chs"); CreateForkForDirW(L"E:\\开发项目", L"E:\\test");}