HP-UX Reference (11i v2 04/09) - 4 File Formats (vol 8)

f
fs_vxfs(4) fs_vxfs(4)
NAME
fs_vxfs - format of a VxFS file system volume
SYNOPSIS
#include <sys/types.h>
#include <sys/param.h>
#include <sys/fs/vx_fs.h>
DESCRIPTION
The VxFS super-block always begins at byte offset 8192 from the start of the file system. The super-block
location is fixed so that various system utilities know where to locate it.
Super-block fields contain the following fundamental sizes and offsets:
fs_bsize The block size of the file system. VxFS supports block sizes of 1024, 2048, 4096,
and 8192 bytes. The default block size depends on the size of the file system
when you create it. See the bsize option in mkfs_vxfs (1M) for specific values.
fs_ctime The creation date of the file system. The
time() system call supplies the time.
fs_defiextsize
The default size, in blocks, for indirect data extents. Currently set to 64 by
default.
fs_dsize The number of data blocks in the file system. A data block is a block which may
be allocated to a file in the file system.
fs_ectime A placeholder in instances when the creation date for a file system is expanded
for more precision. Currently zero.
fs_immedlen The size, in bytes, of the immediate data area in each inode. Currently 96.
fs_logend The block address of the last log area block. You can specify the log area size
with the mkfs command. If not specified, the default size is 256 blocks for a file
system less than 8 megabytes in size, 1024 blocks for a file system from 8 mega-
bytes to 512 megabytes, and 16384 blocks for file systems greater than 512
megabytes in size. For smaller file systems, the default is reduced to avoid wast-
ing space.
fs_logstart The block address of the first log area block. Currently two.
fs_magic The magic number (VX_MAGIC) for the file system. This number identifies the
file system as a VxFS file system type.
fs_nau The number of file system allocation units.
fs_ndaddr The number of direct extents supported by the VX_EXT4 mapping type (see the
section describing inode list). Currently 10.
fs_size The number of blocks, of size fs_bsize , in the file system. fs_size is an
unsigned 32-bit number, so the maximum number of blocks in a VxFS file system
is limited to 32 bits.
fs_version The version number (VX_VERSION) of the file system disk layout.
The preceding fields define the size and makeup of the file system. To reduce the calculations required in
utilities, some of the values are derived from the fundamental values and placed in the super-block.
The super-block contains the following derived offsets:
fs_aublocks The number of data blocks in an allocation unit.
fs_aufirst The address, in blocks, of the first allocation unit. There can be a gap between
the end of the intent log and the first allocation unit. This gap is used to align
the first allocation unit on a desired boundary.
fs_auemlen The length of a free extent map in blocks.
fs_aulen The length of an allocation unit in blocks.
fs_aupad The length, in blocks, of the allocation unit alignment padding.
fs_bmask A mask value such that (byte_offset & fs_bmask ) rounds the offset to the nearest
smaller block boundary.
Section 4−−52 Hewlett-Packard Company − 1 − HP-UX 11i Version 2: September 2004