HP-UX Reference (11i v1 00/12) - 4 File Formats (vol 8)

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STANDARD Printed by: Nora Chuang [nchuang] STANDARD
/build/1111/BRICK/man4/!!!intro.4
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f
fs(4) fs(4)
Cylinder-Group-Related Limits
Each cylinder keeps track of the availability of blocks at different rotational positions, so that sequential
blocks can be laid out with minimum rotational latency. NRPOS is the number of rotational positions
which are distinguished. For example, with NRPOS 8 the resolution of the summary information is 2ms for
a typical 3600 rpm drive.
fs_rotdelay gives the minimum number of milliseconds to initiate another disk transfer on the same
cylinder. It is used in determining the rotationally optimal layout for disk blocks within a file; the default
value for fs_rotdelay is 2ms. Suggested values of fs_rotdelay for different disks can be found in
the system administrator’s manual.
Each file system has a statically allocated number of inodes. An inode is allocated for each NBPI bytes of
disk space. The inode allocation strategy is extremely conservative.
MAXIPG bounds the number of inodes per cylinder group, and is needed only to keep the structure simpler
by having only a single variable size element (the free bit map).
Important Note: MAXIPG must be a multiple of INOPB(fs).
MINBSIZE is the smallest allowable block size. With a MINBSIZE of 4096, it is possible to create files of
size 2
32
with only two levels of indirection. MINBSIZE must be big enough to hold a cylinder group block,
thus
MINBSIZE must always be greater than sizeof(struct cg)
. Note that super blocks are never
more than size
SBSIZE.
The path name on which the file system is mounted is maintained in fs_fsmnt. MAXMNTLEN
defines
the amount of space allocated in the super block for this name. The limit on the amount of summary infor-
mation per file system is defined by
MAXCSBUFS. It is currently parameterized for a maximum of two mil-
lion cylinders.
Per cylinder group information is summarized in blocks allocated from the first cylinder group’s data blocks.
These blocks are read in from fs_csaddr (size fs_cssize) in addition to the super block.
Important Note: sizeof (struct csum) must be a power of two in order for the fs_cs macro to
work.
The two possible values for
fs_magic are FS_MAGIC, the default magic number for an HFS file system
with a fixed-size directory format that limits file name length to
DIRSIZ (14), and FS_MAGIC_LFN , the
magic number of a file system using a variable-size directory format that supports file names of up to
MAXNAMLEN (255) characters in length.
Super Block for a File System:
MAXBPC bounds the size of the rotational layout tables and is limited by the fact that the super block is of
size SBSIZE. The size of these tables is inversely proportional to the block size of the file system. The size
of the tables is increased when sector sizes are not powers of two, as this increases the number of cylinders
included before the rotational pattern repeats (fs_cpc). The size of the rotational layout tables is derived
from the number of bytes remaining in (struct fs).
MAXBPG bounds the number of blocks of data per cylinder group, and is limited by the fact that cylinder
groups are, at most, one block. The size of the free block table is derived from the size of blocks and the
number of remaining bytes in the cylinder group structure (struct cg).
inode:
The inode is the focus of all file activity in the HP-UX file system. There is a unique inode allocated for each
active file, each continuation inode, each current directory, each mounted-on file, text file, and the root. An
inode is ‘‘named’’ by its device-and-i-number pair. For the format of an inode and its flags, see inode(4).
DEPENDENCIES
Series 700
Series 700 systems support only one section per volume. Thus, there can only be one file system on each
volume and the first 8 Kbytes of a file system is the boot area. This area contains the
LIF volume header,
the directory that defines the contents of the volume, and the bootstrapping program.
AUTHOR
fs was developed by HP and the University of California, Berkeley.
Section 4−−56 − 3 − HP-UX Release 11i: December 2000
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