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diskpart(8) [bsd man page]

DISKPART(8)						      System Manager's Manual						       DISKPART(8)

diskpart - calculate default disk partition sizes SYNOPSIS
/usr/sbin/diskpart [ -p ] [ -d ] disk-type DESCRIPTION
Diskpart is used to calculate the disk partition sizes based on the default rules used at Berkeley. If the -p option is supplied, tables suitable for inclusion in a device driver are produced. If the -d option is supplied, an entry suitable for inclusion in the disk descrip- tion file /etc/disktab is generated; c.f. disktab(5). On disks that use bad144-style bad-sector forwarding, space is left in the last partition on the disk for a bad sector forwarding table. The space reserved is one track for the replicated copies of the table and suffi- cient tracks to hold a pool of 126 sectors to which bad sectors are mapped. For more information, see bad144(8). The disk partition sizes are based on the total amount of space on the disk as given in the table below (all values are supplied in units of 512 byte sectors). The `c' partition is, by convention, used to access the entire physical disk. The device driver tables include the space reserved for the bad sector forwarding table in the `c' partition; those used in the disktab and default formats exclude reserved tracks. In normal operation, either the `g' partition is used, or the `d', `e', and `f' partitions are used. The `g' and `f' partitions are variable-sized, occupying whatever space remains after allocation of the fixed sized partitions. If the disk is smaller than 20 Megabytes, then diskpart aborts with the message ``disk too small, calculate by hand''. Partition 20-60 MB 61-205 MB 206-355 MB 356+ MB a 15884 15884 15884 15884 b 10032 33440 33440 66880 d 15884 15884 15884 15884 e unused 55936 55936 307200 h unused unused 291346 291346 If an unknown disk type is specified, diskpart will prompt for the required disk geometry information. SEE ALSO
disktab(5), bad144(8) BUGS
Certain default partition sizes are based on historical artifacts (e.g. RP06), and may result in unsatisfactory layouts. When using the -d flag, alternate disk names are not included in the output. 4th Berkeley Distribution November 17, 1996 DISKPART(8)

Check Out this Related Man Page

chpt(8) 						      System Manager's Manual							   chpt(8)

       chpt - change a disk partition table

       /etc/chpt [ -a ] [ -d ] [ -q ] [ -v ] [ [ -px offset size ] ... ] device

       The  command  lets  you alter the partition sizes of a disk pack.  Using you can tailor your system disks and their partitions to suit your
       system's individual needs.

       If you want to create a file system on a partition that has been modified, you must use

       The standard procedure to change a partition table is:

       1. Look at the current partition table using the -q option.

       2. If a file system does not exist on the a partition, create one using the command.

	  If a file system exists on the a partition but does not contain a partition table in its superblock, copy the partition table  from  the
	  driver to the superblock using the command with the -a option.

       3. Change the partition offsets and sizes using the -px option.	You can change all the partitions for one pack on one command line.

       The  device  must be either the a or c partition of the raw device, depending upon where the file system resides.  For example, if the file
       system resides in the a partition of an RM05 in drive 0, device is rhp0a.

       A file system must exist on the a or c partition of the pack.  If you do not have a file system there, create one using

       -a    Copies the partition table in the device driver to the disk pack.

       -d    Copies the default partition table to the disk pack and to the current partition table in the driver.  The default partition table is
	     the table that was built with the disk driver.

       -q    Runs without modifying the partition tables.  This prints the partition table of the specified disk pack.	It prints the default par-
	     tition table in the driver if there is no partition table on the disk pack.

       -v    Prints verbose messages showing the progress of

       -px   Changes the parameters of partition x on the disk pack to the specified offset and size.  x is the partition you are modifying (a, b,
	     c,  d,  e, f, g, or h).  Offset is the new beginning sector, and size is the new total number of sectors of the partition being modi-

       This example shows how to change the partition table on an RM05 disk pack in drive 1.  The commands in this example change the the size	of
       the h partition to include the g partition.  Comments are in parenthesis to the right of commands.
       % chpt -q /dev/rhp1a	(view partition table)
       No partition table found in superblock...
       using default table from device driver.
       Current partition table:
       partition       bottom	    top      size    overlap
	   a		    0	  15883     15884    c
	   b		16416	  49855     33440    c
	   c		    0	 500383    500384    a,b,d,e,f,g,h
	   d	       341696	 357579     15884    c,g
	   e	       358112	 414047     55936    c,g
	   f	       414048	 500287     86240    c,g
	   g	       341696	 500287    158592    c,d,e,f
	   h		49856	 341201    291346    c
       In  all	of  the tables generated by bottom is the offset (starting sector), top is the ending sector, and size is the number of sectors in
       the partition.  The overlap is the other sectors that are partially or entirely included in the partition.
       % bc		   (basic calculator)
       500287-49856	   (top of g minus bottom of h)
       450431+1 	   (add 1 because it is zero-based)
       450432		   (size of new h partition)

       From the query, you can see that there is no partition table in the superblock of the a partition.  If this is because  there  is  no  file
       system in the a partition, run the command to create one.

       For this example, assume that there is a file system in the a partition of the disk, but the file system does not contain a partition table
       in its superblock.  Therefore, run with the -a option to copy the partition table in the driver to the superblock of the a partition.
       % chpt -a /dev/rhp1a	(add table to a partition)

       Now you have a partition table to change.
       % chpt -v -ph 49856 450432 /dev/rhp1a   (change h)
       New partition table:
       partition       bottom  top     size    overlap
	   a		    0	15883	15884  c
	   b		16416	49855	33440  c
	   c		    0  500383  500384  a,b,d,e,f,g,h
	   d	       341696  357579	15884  c,g,h
	   e	       358112  414047	55936  c,g,h
	   f	       414048  500287	86240  c,g,h
	   g	       341696  500287  158592  c,d,e,f,h
	   h		49856  500287  450432  c,d,e,f,g

       Changing partition tables indiscriminately can result in losing large amounts of data.

       Check for file systems on all the partitions of the disk before using the -p option.  If a  file  system  exists  whose	partition  may	be
       destroyed, copy it to a backup medium.  After you have changed the partitions, restore the backed up file system.

       You must have superuser privileges to use

       You  can not shrink or change the offset of a partition with a file system mounted on it or with an open file descriptor on the entire par-

       You can not change the offset of the a partition.

See Also
       ioctl(2), disktab(5), fsck(8), mkfs(8), newfs(8)
       Guide to System Disk Maintenance


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