HFS+ volume header

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Description

Each HFS Plus volume contains a volume header 1024 bytes from the start of the volume. The volume header contains information about the volume as a whole, including the location of other key structures in the volume. A copy of the volume header, the alternate volume header, is stored starting 1024 bytes before the end of the volume. The alternate volume header is intended for use solely by disk repair utilities.

Hexdump [BIN] [TXT]

00000000 48 2b 00 04 00 00 21 00 48 46 53 4a 00 00 00 02 |H+....!.HFSJ....|
00000010 c3 75 dd 2d c3 75 b3 70 00 00 00 00 c3 75 b2 fd |.u.-.u.p.....u..|
00000020 00 00 00 0b 00 00 00 04 00 00 10 00 00 00 28 f6 |..............(.|
00000030 00 00 1f fd 00 00 0c 21 00 01 00 00 00 01 00 00 |.......!........|
00000040 00 00 00 21 00 00 00 6e 00 00 00 00 00 00 00 01 |...!...n........|
00000050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00000060 00 00 00 00 00 00 00 00 54 c0 89 b3 26 cc a5 b9 |........T...&...|
00000070 00 00 00 00 00 00 10 00 00 00 10 00 00 00 00 01 |................|
00000080 00 00 00 01 00 00 00 01 00 00 00 00 00 00 00 00 |................|
00000090 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000000a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000000b0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000000c0 00 00 00 00 00 05 10 00 00 05 10 00 00 00 00 51 |...............Q|
000000d0 00 00 08 03 00 00 00 51 00 00 00 00 00 00 00 00 |.......Q........|
000000e0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000000f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00000100 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00000110 00 00 00 00 00 05 10 00 00 05 10 00 00 00 00 51 |...............Q|
00000120 00 00 08 54 00 00 00 51 00 00 00 00 00 00 00 00 |...T...Q........|
00000130 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00000140 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00000150 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00000160 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00000170 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00000180 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00000190 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000001a0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000001b0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000001c0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000001d0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000001e0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
000001f0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 |................|
00000200

C struct [TXT]

struct HFSPlusVolumeHeader {
 UInt16 signature;
 UInt16 version;
 UInt32 attributes;
 UInt32 lastMountedVersion;
 UInt32 journalInfoBlock;
 
 UInt32 createDate;
 UInt32 modifyDate;
 UInt32 backupDate;
 UInt32 checkedDate;
 
 UInt32 fileCount;
 UInt32 folderCount;
 
 UInt32 blockSize;
 UInt32 totalBlocks;
 UInt32 freeBlocks;
 
 UInt32 nextAllocation;
 UInt32 rsrcClumpSize;
 UInt32 dataClumpSize;
 HFSCatalogNodeID nextCatalogID;
 
 UInt32 writeCount;
 UInt64 encodingsBitmap;
 
 UInt32 finderInfo[8];
 
 HFSPlusForkData allocationFile;
 HFSPlusForkData extentsFile;
 HFSPlusForkData catalogFile;
 HFSPlusForkData attributesFile;
 HFSPlusForkData startupFile;
};
typedef struct HFSPlusVolumeHeader HFSPlusVolumeHeader;

Offsets in the HFS+ volume header

+0x000	signature		0x482b	[H+]
+0x002	version		0x0004	[4]
+0x004	attributes		0x00002100	[0000 0000 0000 0000 0010 0001 0000 0000b]
+0x008	lastMountedVersion		0x446534a	[HFSJ]
+0x00C	journalInfoBlock		0x00000002	[2]
+0x010	createDate		0xc375dd2d	[]
+0x014	modifyDate		0xc375b370	[]
+0x018	backupDate		0x00000000	[]
+0x01C	checkedDate		0xc375b2fd	[]
+0x020	fileCount		0x0000000b	[11]
+0x024	folderCount		0x00000004	[4]
+0x028	blockSize		0x00001000	[4096]
+0x02C	totalBlocks		0x000028f6	[10486]
+0x030	freeBlocks		0x00001ffd	[8189]
+0x034	nextAllocation		0x00000c21	[3105]
+0x038	rsrcClumpSize		0x00010000	[65536]
+0x03C	dataClumpSize		0x00010000	[65536]
+0x040	nextCatalogID		0x0000021	[33]
+0x044	writeCount		0x0000006e	[110]
+0x048	encodingsBitmap		0x0000000000000001	[]
+0x050	finderInfo	finderInfo[0]	0x00000000	[0]
+0x054		finderInfo[1]	0x00000000	[0]
+0x058		finderInfo[2]	0x00000000	[0]
+0x05C		finderInfo[3]	0x00000000	[0]
+0x060		finderInfo[4]	0x00000000	[0]
+0x064		finderInfo[5]	0x00000000	[0]
+0x068		finderInfo[6]	0x54c089b3	[0x54c089b3]
+0x06C		finderInfo[7]	0x26cca5b9	[0x26cca5b9]
+0x070	allocationFile	logicalSize	0x0000000000001000	[4096]
+0x078		clumpSize	0x00001000	[4096]
+0x07C		totalBlocks	0x00000001	[1]
+0x080		extent[0].startBlock	0x00000001	[1]
+0x084		extent[0].blockCount	0x00000001	[1]
+0x088		extent[1].startBlock	0x00000000	[0]
+0x08C		extent[1].blockCount	0x00000000	[0]
+0x090		extent[2].startBlock	0x00000000	[0]
+0x094		extent[2].blockCount	0x00000000	[0]
+0x098		extent[3].startBlock	0x00000000	[0]
+0x09C		extent[3].blockCount	0x00000000	[0]
+0x0A0		extent[4].startBlock	0x00000000	[0]
+0x0A4		extent[4].blockCount	0x00000000	[0]
+0x0A8		extent[5].startBlock	0x00000000	[0]
+0x0AC		extent[5].blockCount	0x00000000	[0]
+0x0B0		extent[6].startBlock	0x00000000	[0]
+0x0B4		extent[6].blockCount	0x00000000	[0]
+0x0B8		extent[7].startBlock	0x00000000	[0]
+0x0BC		extent[7].blockCount	0x00000000	[0]
+0x0C0	extentsFile	logicalSize	0x0000000000051000	[331776]
+0x0C8		clumpSize	0x00051000	[331776]
+0x0CC		totalBlocks	0x00000051	[81]
+0x0D0		extent[0].startBlock	0x00000803	[2051]
+0x0D4		extent[0].blockCount	0x00000051	[81]
+0x0D8		extent[1].startBlock	0x00000000	[0]
+0x0DC		extent[1].blockCount	0x00000000	[0]
+0x0E0		extent[2].startBlock	0x00000000	[0]
+0x0E4		extent[2].blockCount	0x00000000	[0]
+0x0E8		extent[3].startBlock	0x00000000	[0]
+0x0EC		extent[3].blockCount	0x00000000	[0]
+0x0F0		extent[4].startBlock	0x00000000	[0]
+0x0F4		extent[4].blockCount	0x00000000	[0]
+0x0F8		extent[5].startBlock	0x00000000	[0]
+0x0FC		extent[5].blockCount	0x00000000	[0]
+0x100		extent[6].startBlock	0x00000000	[0]
+0x104		extent[6].blockCount	0x00000000	[0]
+0x108		extent[7].startBlock	0x00000000	[0]
+0x10C		extent[7].blockCount	0x00000000	[0]
+0x110	catalogFile	logicalSize	0x0000000000051000	[331776]
+0x118		clumpSize	0x00051000	[331776]
+0x11C		totalBlocks	0x00000051	[81]
+0x120		extent[0].startBlock	0x00000854	[2132]
+0x124		extent[0].blockCount	0x00000051	[81]
+0x128		extent[1].startBlock	0x00000000	[0]
+0x12C		extent[1].blockCount	0x00000000	[0]
+0x130		extent[2].startBlock	0x00000000	[0]
+0x134		extent[2].blockCount	0x00000000	[0]
+0x138		extent[3].startBlock	0x00000000	[0]
+0x13C		extent[3].blockCount	0x00000000	[0]
+0x140		extent[4].startBlock	0x00000000	[0]
+0x144		extent[4].blockCount	0x00000000	[0]
+0x148		extent[5].startBlock	0x00000000	[0]
+0x14C		extent[5].blockCount	0x00000000	[0]
+0x150		extent[6].startBlock	0x00000000	[0]
+0x154		extent[6].blockCount	0x00000000	[0]
+0x158		extent[7].startBlock	0x00000000	[0]
+0x15C		extent[7].blockCount	0x00000000	[0]
+0x160	attributesFile	logicalSize	0x0000000000000000	[0]
+0x168		clumpSize	0x00000000	[0]
+0x16C		totalBlocks	0x00000000	[0]
+0x170		extent[0].startBlock	0x00000000	[0]
+0x174		extent[0].blockCount	0x00000000	[0]
+0x178		extent[1].startBlock	0x00000000	[0]
+0x17C		extent[1].blockCount	0x00000000	[0]
+0x180		extent[2].startBlock	0x00000000	[0]
+0x184		extent[2].blockCount	0x00000000	[0]
+0x188		extent[3].startBlock	0x00000000	[0]
+0x18C		extent[3].blockCount	0x00000000	[0]
+0x190		extent[4].startBlock	0x00000000	[0]
+0x194		extent[4].blockCount	0x00000000	[0]
+0x198		extent[5].startBlock	0x00000000	[0]
+0x19C		extent[5].blockCount	0x00000000	[0]
+0x1A0		extent[6].startBlock	0x00000000	[0]
+0x1A4		extent[6].blockCount	0x00000000	[0]
+0x1A8		extent[7].startBlock	0x00000000	[0]
+0x1AC		extent[7].blockCount	0x00000000	[0]
+0x1B0	startupFile	logicalSize	0x0000000000000000	[0]
+0x1B8		clumpSize	0x00000000	[0]
+0x1BC		totalBlocks	0x00000000	[0]
+0x1C0		extent[0].startBlock	0x00000000	[0]
+0x1C4		extent[0].blockCount	0x00000000	[0]
+0x1C8		extent[1].startBlock	0x00000000	[0]
+0x1CC		extent[1].blockCount	0x00000000	[0]
+0x1D0		extent[2].startBlock	0x00000000	[0]
+0x1D4		extent[2].blockCount	0x00000000	[0]
+0x1D8		extent[3].startBlock	0x00000000	[0]
+0x1DC		extent[3].blockCount	0x00000000	[0]
+0x1E0		extent[4].startBlock	0x00000000	[0]
+0x1E4		extent[4].blockCount	0x00000000	[0]
+0x1E8		extent[5].startBlock	0x00000000	[0]
+0x1EC		extent[5].blockCount	0x00000000	[0]
+0x1F0		extent[6].startBlock	0x00000000	[0]
+0x1F4		extent[6].blockCount	0x00000000	[0]
+0x1F8		extent[7].startBlock	0x00000000	[0]
+0x1FC		extent[7].blockCount	0x00000000	[0]

Fields of the HFS+ volume header

signature

description: The volume signature.

possible values:

'BD'	HFS volume
'H+'	HFS+ volume
'HX'	HFSX volume

version

description: The version of the volume format.

possible values:

4	HFS+ volume
5	HFSX volume

attributes

description: The attributes field of a volume header is treated as a set of one-bit flags.

possible values:

Bit	Attribute name	Description
0 - 7	Reserved
8	kHFSVolumeUnmountedBit	This bit is set if the volume was correctly flushed before being unmounted or ejected.
9	kHFSVolumeSparedBlocksBit	This bit is set if there are any records in the extents overflow file for bad blocks (belonging to file ID kHFSBadBlockFileID).
10	kHFSVolumeNoCacheRequiredBit	This bit is set if the blocks from this volume should not be cached.
11	kHFSBootVolumeInconsistentBit	This bit is similar to kHFSVolumeUnmountedBit, but inverted in meaning.
12	kHFSCatalogNodeIDsReusedBit	This bit is set when the nextCatalogID field overflows 32 bits, forcing smaller catalog node IDs to be reused. When this bit is set, it is common (and not an error) for catalog records to exist with IDs greater than or equal to nextCatalogID.
13	kHFSVolumeJournaledBit	If this bit is set, the volume has a journal.
14	Reserved
15	kHFSVolumeSoftwareLockBit	This bit is set if the volume is write-protected due to a software setting. Any implementations must refuse to write to a volume with this bit set.
16 - 31	Reserved

lastMountedVersion

description: A value which uniquely identifies the implementation that last mounted this volume for writing. Any code which modifies the on disk structures must also set this field to a unique value which identifies that code. Third-party implementations of HFS Plus should place a registered creator code in this field.

possible values:

'8.10'	Mac OS 8.1 to 9.2.2
'10.0'	Mac OS X
'HFSJ'	Journaled volume (including HFSX) in Mac OS X

journalInfoBlock

description: The allocation block number of the allocation block which contains the JournalInfoBlock for this volume's journal. This field is valid only if bit kHFSVolumeJournaledBit is set in the attribute field; otherwise, this field is reserved.

createDate

description: The date and time when the volume was created.

modifyDate

description: The date and time when the volume was last modified.

backupDate

description: The date and time when the volume was last backed up.

checkedDate

description: The date and time when the volume was last checked for consistency.

fileCount

description: The total number of files on the volume. The fileCount field does not include the special files. It should equal the number of file records found in the catalog file.

folderCount

description: The total number of folders on the volume. The folderCount field does not include the root folder. It should equal the number of folder records in the catalog file, minus one (since the root folder has a folder record in the catalog file).

blockSize

description: The allocation block size, in bytes.

totalBlocks

description: The total number of allocation blocks on the disk.

freeBlocks

description: The total number of unused allocation blocks on the disk.

nextAllocation

description: Start of next allocation search. The nextAllocation field is used by Mac OS as a hint for where to start searching for free allocation blocks when allocating space for a file. It contains the allocation block number where the search should begin.

rsrcClumpSize

description: The default clump size for resource forks, in bytes.

dataClumpSize

description: The default clump size for data forks, in bytes.

nextCatalogID

description: The next unused catalog ID.

writeCount

description: This field is incremented every time a volume is mounted.

encodingsBitmap

description: This field keeps track of the text encodings used in the file and folder names on the volume.

finderInfo

description: This array of 32-bit items contains information used by the Mac OS Finder, and the system software boot process.

Item	Description
finderInfo[0]	To contain the directory ID of the directory containing the bootable system. It is zero if there is no bootable system on the volume.
finderInfo[1]	To contain the parent directory ID of the startup application (for example, Finder), or zero if the volume is not bootable.
finderInfo[2]	To contain the directory ID of a directory whose window should be displayed in the Finder when the volume is mounted, or zero if no directory window should be opened.
finderInfo[3]	To contain the directory ID of a bootable Mac OS 8 or 9 System Folder, or zero if there isn't one.
finderInfo[4]	Reserved.
finderInfo[5]	To contain the directory ID of a bootable Mac OS X system, or zero if there is no bootable Mac OS X system on the volume.
finderInfo[6]	To contain a first half of a 64-bit unique volume identifier.
finderInfo[7]	To contain a second half of a 64-bit unique volume identifier.

allocationFile

description: Information about the location and size of the allocation file.

Item	Description
logicalSize	The size, in bytes, of the allocation file.
clumpSize	The fork's clump size for the allocation file.
totalBlocks	The total number of allocation blocks used by the allocation file.
extent[0].startBlock	The first allocation block for the extent[0] of the allocation file.
extent[0].blockCount	The length, in allocation blocks, of the extent[0] of the allocation file.
extent[1].startBlock	The first allocation block for the extent[1] of the allocation file.
extent[1].blockCount	The length, in allocation blocks, of the extent[1] of the allocation file.
extent[2].startBlock	The first allocation block for the extent[2] of the allocation file.
extent[2].blockCount	The length, in allocation blocks, of the extent[2] of the allocation file.
extent[3].startBlock	The first allocation block for the extent[3] of the allocation file.
extent[3].blockCount	The length, in allocation blocks, of the extent[3] of the allocation file.
extent[4].startBlock	The first allocation block for the extent[4] of the allocation file.
extent[4].blockCount	The length, in allocation blocks, of the extent[4] of the allocation file.
extent[5].startBlock	The first allocation block for the extent[5] of the allocation file.
extent[5].blockCount	The length, in allocation blocks, of the extent[5] of the allocation file.
extent[6].startBlock	The first allocation block for the extent[6] of the allocation file.
extent[6].blockCount	The length, in allocation blocks, of the extent[6] of the allocation file.
extent[7].startBlock	The first allocation block for the extent[7] of the allocation file.
extent[7].blockCount	The length, in allocation blocks, of the extent[7] of the allocation file.

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