159 lines
5.8 KiB
Groff
159 lines
5.8 KiB
Groff
.TH HD 4
|
|
.SH NAME
|
|
hd \- winchester hard disk
|
|
.SH DESCRIPTION
|
|
The
|
|
.B hd*
|
|
family of devices refer to the Winchester hard disk drivers for
|
|
the IBM XT, AT and PS/2 machines, but may also refer to the generic (and
|
|
slower) BIOS based hard disk driver. These disks are arrays of 512 byte
|
|
sectors, although Minix always works with two sectors at a time due to its
|
|
1024 byte block size. You can read or write any number of bytes however,
|
|
Minix takes care of cutting and pasting incomplete blocks together.
|
|
.PP
|
|
The devices may be divided into three classes:
|
|
.sp
|
|
.RS
|
|
The devices with a minor device number that is a multiple of 5, i.e.
|
|
.B hd0
|
|
or
|
|
.BR hd5 ,
|
|
refer to the whole hard disk 0 and 1. Through these devices one has access
|
|
to any block on the hard disk. Most notably the partition table, that can
|
|
be found in the first sector of the disk.
|
|
.sp
|
|
The devices with a minor device number that is not a multiple of 5, i.e.
|
|
.BR hd1 ,
|
|
.BR hd2 ,
|
|
\&...,
|
|
.BR hd6 ,
|
|
\&..., refer to primary partitions of the lower numbered whole hard disk
|
|
device. These devices normally contain MS-DOS or Minix file systems.
|
|
/dev/hd1 is often the MS-DOS C: drive.
|
|
.sp
|
|
Minor devices from 128 up may refer to Minix subpartitions within primary
|
|
partitions if a subpartition table has been placed in a Minix primary
|
|
partition. The subpartitions of
|
|
.B hd3
|
|
for instance, are named
|
|
.B hd3a
|
|
through
|
|
.BR hd3d .
|
|
Their minor device numbers may be calculated as
|
|
128 + 16*drive + 4*partition + subpartition, counting the partitions
|
|
from zero.
|
|
.PP
|
|
If a primary partition is an extended partition then up to four logical
|
|
partitions can be accessed as subpartitions of that extended partition.
|
|
This allows one to access foreign file systems of other operating systems,
|
|
Minix file systems are not normally placed in logical partitions.
|
|
.SH PARTITIONING
|
|
The first sector of a drive (or partition for subpartitioning) contains the
|
|
partition table at byte offset 446. This is what each of the four entries
|
|
looks like as defined in <ibm/partition.h>:
|
|
.sp
|
|
.nf
|
|
.ta +2n +29n +37n
|
|
/* Description of entry in the partition table. */
|
|
|
|
struct part_entry {
|
|
unsigned char bootind; /* boot indicator 0/ACTIVE_FLAG */
|
|
unsigned char start_head; /* head value for first sector */
|
|
unsigned char start_sec; /* sector value + high 2 cyl bits */
|
|
unsigned char start_cyl; /* low 8 cylinder bits */
|
|
unsigned char sysind; /* system indicator */
|
|
unsigned char last_head; /* h/s/c for the last sector */
|
|
unsigned char last_sec;
|
|
unsigned char last_cyl;
|
|
unsigned long lowsec; /* logical first sector */
|
|
unsigned long size; /* size of partition in sectors */
|
|
};
|
|
|
|
.ta +24n +7n +37n
|
|
#define ACTIVE_FLAG 0x80 /* value for active in bootind field */
|
|
#define NR_PARTITIONS 4 /* number of entries in table */
|
|
#define PART_TABLE_OFF 0x1BE /* offset of table in boot sector */
|
|
|
|
/* Partition types (sysind). */
|
|
#define MINIX_PART 0x81 /* Minix partition type */
|
|
#define NO_PART 0x00 /* unused entry */
|
|
#define OLD_MINIX_PART 0x80 /* created before 1.4b, obsolete */
|
|
#define EXT_PART 0x05 /* extended partition */
|
|
.fi
|
|
.PP
|
|
The cylinder numbers are encoded in a very strange way, bits 8 and 9 are
|
|
in the high two bits of the sector number. The sector numbers count from 1,
|
|
not 0! More useful are the lowsec and size fields however, they simply give
|
|
the location of the partition as an absolute sector offset and length within
|
|
the drive.
|
|
.PP
|
|
The partition table entry defined above is specific to IBM type disks. The
|
|
device drivers use another partition entry structure to pass information on
|
|
a partition. This is what <minix/partition.h> looks like:
|
|
.sp
|
|
.nf
|
|
.ta +2n +25n
|
|
struct partition {
|
|
u64_t base; /* byte offset to the partition start */
|
|
u64_t size; /* number of bytes in the partition */
|
|
unsigned cylinders; /* disk geometry for partitioning */
|
|
unsigned heads;
|
|
unsigned sectors;
|
|
};
|
|
.fi
|
|
.PP
|
|
The base and size fields are the byte offset and length of a partition.
|
|
(These are 64 bit numbers under Minix-vmd, but only 32 bit numbers under
|
|
standard Minix.) The geometry of the disk is also given for the benefit of
|
|
partition table editors. This information can be obtained from an open disk
|
|
device with the call:
|
|
.sp
|
|
.RS
|
|
.ft B
|
|
ioctl(\fIfd\fP, DIOCGETP, &\fIentry\fP);
|
|
.ft R
|
|
.RE
|
|
.sp
|
|
One can change the placement of the device to the lowsec and size fields of
|
|
.I entry
|
|
by using the
|
|
.B DIOCSETP
|
|
call instead. Only the base and size fields are used for
|
|
.BR DIOCSETP .
|
|
.PP
|
|
The partition tables when read from disk by the driver are checked and
|
|
truncated to fit within the primary partition or drive. The first sector
|
|
should be left free for the partition table.
|
|
.PP
|
|
The partition tables are read when the in-use count (opens and mounts)
|
|
changes from 0 to 1. So an idle disk is automatically repartitioned on the
|
|
next access. This means that repartitioning programs only have effect if a
|
|
disk stays in use, unless they reload a changed partition table.
|
|
.SH FILES
|
|
/dev/hd[0\-9], /dev/hd[1\-46\-9][a\-d]
|
|
.SH "SEE ALSO"
|
|
.BR ioctl (2),
|
|
.BR int64 (3),
|
|
.BR part (8),
|
|
.BR repartition (8).
|
|
.SH BUGS
|
|
The subpartitioning is incompatible with the MS-DOS method of extended
|
|
partitions. The latter does not map well to the sparse minor device number
|
|
space.
|
|
.PP
|
|
The primary partition table is sorted by lowsec like MS-DOS does, subpartition
|
|
tables are not. Just think about what happens when you delete a partition in
|
|
the MS-DOS scheme.
|
|
.PP
|
|
Don't move a partition that is mounted or kept open by some process. The
|
|
file system may write cached blocks to the new location.
|
|
.PP
|
|
The BIOS driver is not slow at all on a buffered disk.
|
|
.PP
|
|
Some IDE disks send an interrupt when they spin down under hardware power
|
|
management. The driver acknowledges the interrupt as it is supposed to do by
|
|
reading the status register. The disk then spins up again... You have to
|
|
disable the spin down in the computer setup to fix the problem.
|
|
.SH AUTHOR
|
|
Kees J. Bot (kjb@cs.vu.nl)
|