fs_vxfs - format of a VxFS file system volume
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:
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 the mkfs_vxfs(1M) manual page for specific values.
The creation date of the file system. The time system call supplies the time.
The default size, in blocks, for indirect data extents. Currently set to 64 by default.
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.
The size, in bytes, of the immediate data area in each inode. Currently 96.
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 megabytes 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 wasting space. The maximum log size is 256 megabytes for disk layout Version 6 and 7, and 16 megabytes for disk layout Version 4.
The block address of the first log area block. Currently two.
The magic number ( VX_MAGIC ) for the file system. This number identifies the file system as a VxFS file system type.
The number of file system allocation units.
The number of direct extents supported by the VX_EXT4 mapping type. See the section describing the inode list. Currently 10.
The number of blocks, of size fs_bsize, in the file system. fs_size is an unsigned 64-bit number, so the maximum number of blocks in a VxFS file system is limited to 64 bits.
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:
The number of data blocks in an allocation unit.
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.
The length of a free extent map in blocks.
The length of an allocation unit in blocks.
The length, in blocks, of the allocation unit alignment padding.
A mask value such that (byte_offset & fs_bmask) rounds the offset to the nearest smaller block boundary.
A mask value such that (byte_offset & fs_boffmask) yields the offset from the start of the nearest smaller block boundary.
The log base 2 of fs_bsize. Used to convert a byte offset into a block offset.
The offset, in blocks, of the first data block from the start of an allocation unit. An allocation unit header may contain padding to align the first data block to a specific boundary.
A checksum of the above fields. A macro, VX_FSCHECKSUM, verifies or calculates the checksum.
The offset, in blocks, of the free extent map (emap) from the start of an allocation unit.
The offset, in blocks, of the first data block from the start of the file system.
The offset, in blocks, of the first free extent map (emap) from the start of the file system.
The offset, in blocks, of the first free inode map (imap) from the start of the file system.
The size, in blocks, of an indirect address block. An indirect address block is 8K bytes. This field is set to (8K / fs_bsize).
The offset, in blocks, of the free inode map (imap) from the start of an allocation unit.
The number of inodes in an allocation unit.
The number of inode entries per fs_bsize block in the inode list. The VxFS inode can be 256 or 512 bytes long.
The log base 2 of fs_inopb. Used to convert an inode number into a block offset in the inode list.
The log base 2 of fs_aublocks.
The number of entries in an indirect address extent. An indirect address extent is currently 8192 bytes in length, making the value for fs_nindir 2048.
The preceding fields are initialized when the file system is created and do not change unless the file system is resized. These fields are replicated in each allocation unit header.
The following are additional fields, which are dynamic:
Set to VX_DIRTY when a file system is mounted for read/write access. Set to VX_CLEAN on a umount or successful fsck. The file system cannot be mounted for read/write access unless the fs_clean field is VX_CLEAN.
An array of the current number of free extents of each extent size in the file system.
Disk layout Version 1 through 6 use the fs_logversion field to denote the extop version. Disk layout Version 7 introduces the fs_extopversion field to denote the extop version.
Initial log ID for when the file system is mounted.
The following flags are recognized:
Set when byteswapping is in progress.
Set when an I/O error occurs in file system data.
Set when fileset quotas are on.
Set when a file system requires a full structural check to recover from an error. If this flag is set, a full check is performed after the replay recovery completes.
Set when a full fsck was run since the last mount.
Set when an I/O error occurs in file system metadata.
Set when the file system was mounted with the VX_MS_NOLOG option. If this flag is set, then no log replay recovery is performed.
Set when a file system resizing is in progress. If fsck detects this flag, it performs a resize recovery. See fsadm_vxfs(1M) for a description of file system expansion.
Set when there is only one device for the file system.
Set when a file system upgrade is in progress. If fsck detects this flag, it performs an upgrade recovery.
File system name (6 characters). The fs_fname field is not used in disk layout Version 7.
File system pack label (6 characters). The fs_fpack field is not used in disk layout Version 7.
The number of free data blocks.
The version number of the log format. Set by the kernel on each mount to ensure that an instantiation of fsck running log replay understands the log format written by the kernel.
The log format may change with each release, so all file systems should be clean before upgrading to a new release.
Set whenever a mounted file system is modified. It indicates whether the super-block requires rewriting when a sync operation is performed.
Indicates the version of VxFS that last modified the file system.
Last time the super-block was written to disk, indicated as the number of seconds and microseconds that have elapsed since 0:00:00 GMT January 1, 1970.
These fields are set when the file system is created and do not change. They are replicated in each allocation unit header.
A checksum of fields.
The size, in bytes, of a disk inode. Currently 256 bytes.
The number of indirect address levels per inode.
The length, in blocks, of a free inode map in an inode allocation unit.
The size, in blocks, of an inode allocation unit.
The size, in blocks, of the object location table extents pointed to by fs_oltext.
An array of two extent addresses. These extent addresses point to the two replicated copies of the first object location table extent.
fsadm_vxfs(1M), fsck(1M), fsdb(1M), mkfs(1M), mount(2), time(2), inode_vxfs(4)