5 files changed, 30 insertions, 10 deletions
diff --git a/src/Core/VolumeCreator.h b/src/Core/VolumeCreator.h
index fc40f34d..3e051bc7 100644
--- a/src/Core/VolumeCreator.h
+++ b/src/Core/VolumeCreator.h
@@ -21,7 +21,8 @@
 #include <errno.h>
 #endif
 
-#define VC_MIN_BTRFS_VOLUME_SIZE 114294784ULL
+#define VC_MIN_LARGE_BTRFS_VOLUME_SIZE 114294784ULL
+#define VC_MIN_SMALL_BTRFS_VOLUME_SIZE 16777216ULL
 
 namespace VeraCrypt
 {
diff --git a/src/Main/Forms/VolumeCreationWizard.cpp b/src/Main/Forms/VolumeCreationWizard.cpp
index 4df20301..5d814e89 100644
--- a/src/Main/Forms/VolumeCreationWizard.cpp
+++ b/src/Main/Forms/VolumeCreationWizard.cpp
@@ -258,7 +258,10 @@ namespace VeraCrypt
 
 		case Step::FormatOptions:
 			{
-				VolumeFormatOptionsWizardPage *page = new VolumeFormatOptionsWizardPage (GetPageParent(), VolumeSize, SectorSize,
+				shared_ptr <VolumeLayout> layout ((OuterVolume || SelectedVolumeType != VolumeType::Hidden)? (VolumeLayout*) new VolumeLayoutV2Normal() : (VolumeLayout*) new VolumeLayoutV2Hidden());
+				uint64 filesystemSize = layout->GetMaxDataSize (VolumeSize);
+
+				VolumeFormatOptionsWizardPage *page = new VolumeFormatOptionsWizardPage (GetPageParent(), filesystemSize, SectorSize,
 					SelectedVolumePath.IsDevice() && (OuterVolume || SelectedVolumeType != VolumeType::Hidden), OuterVolume, LargeFilesSupport);
 
 				page->SetPageTitle (_("Format Options"));
@@ -484,6 +487,9 @@ namespace VeraCrypt
 
 					shared_ptr <VolumeInfo> volume = Core->MountVolume (mountOptions);
 					finally_do_arg (shared_ptr <VolumeInfo>, volume, { Core->DismountVolume (finally_arg, true); });
+					
+					shared_ptr <VolumeLayout> layout((volume->Type == VolumeType::Normal)? (VolumeLayout*) new VolumeLayoutV2Normal() : (VolumeLayout*) new VolumeLayoutV2Hidden());
+					uint64 filesystemSize = layout->GetMaxDataSize (VolumeSize);
 
 					Thread::Sleep (2000);	// Try to prevent race conditions caused by OS
 
@@ -527,7 +533,14 @@ namespace VeraCrypt
 						args.push_back ("-f");
 
 					if (SelectedFilesystemType == VolumeCreationOptions::FilesystemType::Btrfs)
+					{
 						args.push_back ("-f");
+						if (filesystemSize < VC_MIN_LARGE_BTRFS_VOLUME_SIZE)
+						{
+							// use mixed mode for small BTRFS volumes
+							args.push_back ("-M");
+						}
+					}
 
 					args.push_back (string (virtualDevice));
 
diff --git a/src/Main/Forms/VolumeFormatOptionsWizardPage.cpp b/src/Main/Forms/VolumeFormatOptionsWizardPage.cpp
index 30f8c6ba..d3bd5216 100644
--- a/src/Main/Forms/VolumeFormatOptionsWizardPage.cpp
+++ b/src/Main/Forms/VolumeFormatOptionsWizardPage.cpp
@@ -17,7 +17,7 @@
 
 namespace VeraCrypt
 {
-	VolumeFormatOptionsWizardPage::VolumeFormatOptionsWizardPage (wxPanel* parent, uint64 volumeSize, uint32 sectorSize, bool enableQuickFormatButton, bool disableNoneFilesystem, bool disable32bitFilesystems)
+	VolumeFormatOptionsWizardPage::VolumeFormatOptionsWizardPage (wxPanel* parent, uint64 filesystemSize, uint32 sectorSize, bool enableQuickFormatButton, bool disableNoneFilesystem, bool disable32bitFilesystems)
 		: VolumeFormatOptionsWizardPageBase (parent)
 	{
 		InfoStaticText->SetLabel (_(
@@ -26,7 +26,7 @@ namespace VeraCrypt
 		if (!disableNoneFilesystem)
 			FilesystemTypeChoice->Append (LangString["NONE"],	(void *) VolumeCreationOptions::FilesystemType::None);
 
-		if (!disable32bitFilesystems && volumeSize <= TC_MAX_FAT_SECTOR_COUNT * sectorSize)
+		if (!disable32bitFilesystems && filesystemSize <= TC_MAX_FAT_SECTOR_COUNT * sectorSize)
 			FilesystemTypeChoice->Append (L"FAT",			(void *) VolumeCreationOptions::FilesystemType::FAT);
 
 #ifdef TC_WINDOWS
@@ -43,9 +43,8 @@ namespace VeraCrypt
 			FilesystemTypeChoice->Append (L"exFAT",				(void *) VolumeCreationOptions::FilesystemType::exFAT);
 		if (VolumeCreationOptions::FilesystemType::IsFsFormatterPresent (VolumeCreationOptions::FilesystemType::Btrfs))
 		{
-			uint64 minVolumeSizeForBtrfs = VC_MIN_BTRFS_VOLUME_SIZE + (uint64) (VC_MAX (TC_TOTAL_VOLUME_HEADERS_SIZE, TC_HIDDEN_VOLUME_HOST_FS_RESERVED_END_AREA_SIZE_HIGH));
-			// minimum size to be able to format as Btrfs is 114294784 bytes
-			if (volumeSize >= minVolumeSizeForBtrfs)
+			// minimum size to be able to format as Btrfs is 16777216 bytes
+			if (filesystemSize >= VC_MIN_SMALL_BTRFS_VOLUME_SIZE)
 				FilesystemTypeChoice->Append (L"Btrfs",				(void *) VolumeCreationOptions::FilesystemType::Btrfs);
 		}
 #elif defined (TC_MACOSX)
@@ -57,7 +56,7 @@ namespace VeraCrypt
 		FilesystemTypeChoice->Append (L"UFS",				(void *) VolumeCreationOptions::FilesystemType::UFS);
 #endif
 
-		if (!disable32bitFilesystems && volumeSize <= TC_MAX_FAT_SECTOR_COUNT * sectorSize)
+		if (!disable32bitFilesystems && filesystemSize <= TC_MAX_FAT_SECTOR_COUNT * sectorSize)
 			SetFilesystemType (VolumeCreationOptions::FilesystemType::FAT);
 		else
 			SetFilesystemType (VolumeCreationOptions::FilesystemType::GetPlatformNative());
diff --git a/src/Main/Forms/VolumeFormatOptionsWizardPage.h b/src/Main/Forms/VolumeFormatOptionsWizardPage.h
index 25ca2b37..b38f6e99 100644
--- a/src/Main/Forms/VolumeFormatOptionsWizardPage.h
+++ b/src/Main/Forms/VolumeFormatOptionsWizardPage.h
@@ -21,7 +21,7 @@ namespace VeraCrypt
 	class VolumeFormatOptionsWizardPage : public VolumeFormatOptionsWizardPageBase
 	{
 	public:
-		VolumeFormatOptionsWizardPage (wxPanel* parent, uint64 volumeSize, uint32 sectorSize, bool enableQuickFormatButton = true, bool disableNoneFilesystem = false, bool disable32bitFilesystems = false);
+		VolumeFormatOptionsWizardPage (wxPanel* parent, uint64 filesystemSize, uint32 sectorSize, bool enableQuickFormatButton = true, bool disableNoneFilesystem = false, bool disable32bitFilesystems = false);
 
 		VolumeCreationOptions::FilesystemType::Enum GetFilesystemType () const;
 		bool IsValid () { return true; }
diff --git a/src/Main/TextUserInterface.cpp b/src/Main/TextUserInterface.cpp
index 95becfdf..0ad0b958 100644
--- a/src/Main/TextUserInterface.cpp
+++ b/src/Main/TextUserInterface.cpp
@@ -810,7 +810,7 @@ namespace VeraCrypt
 		}
 
 		if (options->Filesystem == VolumeCreationOptions::FilesystemType::Btrfs
-			&& (filesystemSize < VC_MIN_BTRFS_VOLUME_SIZE))
+			&& (filesystemSize < VC_MIN_SMALL_BTRFS_VOLUME_SIZE))
 		{
 			throw_err (_("Specified volume size is too small to be used with Btrfs filesystem."));
 		}
@@ -939,7 +939,14 @@ namespace VeraCrypt
 				args.push_back ("-f");
 
 			if (options->Filesystem == VolumeCreationOptions::FilesystemType::Btrfs)
+			{
 				args.push_back ("-f");
+				if (filesystemSize < VC_MIN_LARGE_BTRFS_VOLUME_SIZE)
+				{
+					// use mixed mode for small BTRFS volumes
+					args.push_back ("-M");
+				}
+			}
 
 			args.push_back (string (virtualDevice));