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:
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 the mkfs_vxfs(1M) manual page 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_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 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 later. 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 the inode list. Currently 10. fs_size 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. 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. fs_boffmask A mask value such that (byte_offset & fs_boffmask) yields the offset from the start of the nearest smaller block boundary. fs_bshift The log base 2 of fs_bsize. Used to convert a byte offset into a block offset. fs_bstart 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. fs_checksum A checksum of the above fields. A macro, VX_FSCHECKSUM, verifies or calculates the checksum. fs_emap The offset, in blocks, of the free extent map (emap) from the start of an allocation unit. fs_fbstart The offset, in blocks, of the first data block from the start of the file system. fs_femap The offset, in blocks, of the first free extent map (emap) from the start of the file system. fs_fimap The offset, in blocks, of the first free inode map (imap) from the start of the file system. fs_iaddrlen The size, in blocks, of an indirect address block. An indirect address block is 8K bytes. This field is set to (8K / fs_bsize). fs_imap The offset, in blocks, of the free inode map (imap) from the start of an allocation unit. fs_inopau The number of inodes in an allocation unit. fs_inopb The number of inode entries per fs_bsize block in the inode list. The VxFS inode can be 256 or 512 bytes long. fs_inoshift The log base 2 of fs_inopb. Used to convert an inode number into a block offset in the inode list. fs_maxtier The log base 2 of fs_aublocks. fs_nindir 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:
fs_clean 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. fs_efree An array of the current number of free extents of each extent size in the file system. fs_extopversion 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. fs_firstlogid Initial log ID for when the file system is mounted. fs_flags The following flags are recognized:
VX_BSINPROGRESS Set when byteswapping is in progress. VX_DATAIOERR Set when an I/O error occurs in file system data. VX_FSETQUOTA Set when fileset quotas are on. VX_FULLFSCK 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. VX_FULLFSCKRAN Set when a full fsck was run since the last mount. VX_METAIOERR Set when an I/O error occurs in file system metadata. VX_NOLOG 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. VX_RESIZE 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. VX_SINGLEDEV Set when there is only one device for the file system. VX_UPGRADING Set when a file system upgrade is in progress. If fsck detects this flag, it performs an upgrade recovery. fs_fname File system name (6 characters). The fs_fname field is not used in disk layout Version 7 and later. fs_fpack File system pack label (6 characters). The fs_fpack field is not used in disk layout Version 7 and later. fs_free The number of free data blocks. fs_logversion 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. fs_mod Set whenever a mounted file system is modified. It indicates whether the super-block requires rewriting when a sync operation is performed. fs_modversion Indicates the version of VxFS that last modified the file system. fs_time 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.
fs_checksum2 A checksum of fields. fs_dinosize The size, in bytes, of a disk inode. Currently 256 bytes. fs_dniaddr The number of indirect address levels per inode. fs_iauimlen The length, in blocks, of a free inode map in an inode allocation unit. fs_iausize The size, in blocks, of an inode allocation unit. fs_oltsize The size, in blocks, of the object location table extents pointed to by fs_oltext. 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)