disklabel32/64: Add support for 'T' size specifier.

[dragonfly.git] / sbin / disklabel32 / disklabel32.8

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.\"	@(#)disklabel.8	8.2 (Berkeley) 4/19/94
.\" $FreeBSD: src/sbin/disklabel/disklabel.8,v 1.15.2.22 2003/04/17 17:56:34 trhodes Exp $
.\"
.Dd August 3, 2012
.Dt DISKLABEL32 8
.Os
.Sh NAME
.Nm disklabel32
.Nd read and write 32 bit disk pack label
.Sh SYNOPSIS
.Nm
.Op Fl r
.Ar disk
.Nm
.Fl w
.Op Fl r
.Op Fl n
.Ar disk Ar disktype Ns / Ns Cm auto
.Oo Ar packid Oc
.Nm
.Fl e
.Op Fl r
.Op Fl n
.Ar disk
.Nm
.Fl R
.Op Fl r
.Op Fl n
.Ar disk Ar protofile
.Nm
.Op Fl NW
.Ar disk
.Pp
.Nm
.Fl B
.Oo
.Fl b Ar boot1
.Fl s Ar boot2
.Oc
.Ar disk
.Oo Ar disktype Ns / Ns Cm auto Oc
.Nm
.Fl w
.Fl B
.Op Fl n
.Oo
.Fl b Ar boot1
.Fl s Ar boot2
.Oc
.Ar disk Ar disktype Ns / Ns Cm auto
.Oo Ar packid Oc
.Nm
.Fl R
.Fl B
.Op Fl n
.Oo
.Fl b Ar boot1
.Fl s Ar boot2
.Oc
.Ar disk Ar protofile
.Oo Ar disktype Ns / Ns Cm auto Oc
.Nm
.Fl f Ar slice_start_lba
.Oo Ar options Oc
.Sh DESCRIPTION
The
.Nm
utility
installs, examines or modifies a 32 bit label on a disk drive or pack.
When writing
the label, it can be used to change the drive identification, the disk
partitions on the drive, or to replace a damaged label.
There are several forms
of the command that read (display), install or edit the label on a disk.
In
addition,
.Nm
can install bootstrap code.
.Ss Raw or in-core label
The disk label resides close to or at the beginning of each disk slice.
For faster access, the kernel maintains a copy in core at all times.
By
default, most forms of the
.Nm
command access the in-core copy of the label.
To access the raw (on-disk)
copy, use the
.Fl r
option.
This option allows a label to be installed on a disk without kernel
support for a label, such as when labels are first installed on a system; it
must be used when first installing a label on a disk.
The specific effect of
.Fl r
is described under each command.
.Ss Disk device name
All
.Nm
forms require a disk device name, which should always be the raw
device name representing the disk or slice.
.Dx
uses the following scheme for slice numbering:
If the disk doesn't use GPT (typically laid out by
.Xr gpt 8 ) ,
but e.g.\& MBR (typically laid out by
.Xr fdisk 8 ) ,
then slice 0, e.g.\&
.Pa da0s0 ,
represents the entire disk regardless of any DOS partitioning.
Slice 0 is called the compatibility slice,
and slice 1 and onward, e.g.\&
.Pa da0s1 ,
represents a
.Bx
slice.
If the disk does use GPT, then all slices are
.Bx
slices, slice 0 isn't special, it is just the first slice on the disk.
You do not have to include the
.Pa /dev/
path prefix when specifying the device.
The
.Nm
utility will automatically prepend it.
.Ss Reading the disk label
To examine the label on a disk drive, use
.Nm
without options:
.Pp
.Nm
.Op Fl r
.Ar disk
.Pp
.Ar disk
represents the raw disk in question, and may be in the form
.Pa da0s1
or
.Pa /dev/da0s1 .
It will display all of the parameters associated with the drive and its
partition layout.
Unless the
.Fl r
flag is given,
the kernel's in-core copy of the label is displayed;
if the disk has no label, or the partition types on the disk are incorrect,
the kernel may have constructed or modified the label.
If the
.Fl r
flag is given,
.Nm
reads the label from the raw disk and displays it.
Both versions are usually
identical except in the case where a label has not yet been initialized or
is corrupt.
.Ss Writing a standard label
To write a standard label, use the form
.Pp
.Nm
.Fl w
.Op Fl r
.Op Fl n
.Ar disk Ar disktype Ns / Ns Cm auto
.Oo Ar packid Oc
.Pp
The required arguments to
.Nm
are the drive to be labeled and the drive type as described in the
.Xr disktab 5
file.
The drive parameters and partitions are taken from that file.
If
different disks of the same physical type are to have different partitions, it
will be necessary to have separate disktab entries describing each, or to edit
the label after installation as described below.
The optional argument is a
pack identification string, up to 16 characters long.
The pack id must be
quoted if it contains blanks.
.Pp
If the
.Fl n
flag is given, no data will be written to the device, and instead the
disklabel that would have been written will be printed to stdout.
.Pp
If the
.Fl r
flag is given, the disk sectors containing the label and bootstrap
will be written directly.
A side-effect of this is that any existing bootstrap code will be overwritten
and the disk rendered unbootable.
See the boot options below for a method of
writing the label and the bootstrap at the same time.
If
.Fl r
is not specified,
the existing label will be updated via the in-core copy and any bootstrap
code will be unaffected.
If the disk does not already have a label, the
.Fl r
flag must be used.
In either case, the kernel's in-core label is replaced.
.Pp
For a virgin disk that is not known to
.Xr disktab 5 ,
.Ar disktype
can be specified as
.Cm auto .
In this case, the driver is requested to produce a virgin label for the
disk.
This might or might not be successful, depending on whether the
driver for the disk is able to get the required data without reading
anything from the disk at all.
It will likely succeed for all SCSI
disks, most IDE disks, and vnode devices.
Writing a label to the
disk is the only supported operation, and the
.Ar disk
itself must be provided as the canonical name, i.e.\& not as a full
path name.
.Pp
For most harddisks, a label based on percentages for most partitions (and
one partition with a size of
.Ql * )
will produce a reasonable configuration.
.Pp
PC-based systems have special requirements in order for the BIOS to properly
recognize a
.Dx
disklabel.
Older systems may require what is known as a
.Dq dangerously dedicated
disklabel, which creates a fake DOS partition to work around problems older
BIOSes have with modern disk geometries.
On newer systems you generally want
to create a normal DOS partition using
.Ar fdisk
and then create a
.Dx
disklabel within that slice.
This is described
later on in this page.
.Pp
Installing a new disklabel does not in of itself allow your system to boot
a kernel using that label.
You must also install boot blocks, which is
described later on in this manual page.
.Ss Editing an existing disk label
To edit an existing disk label, use the form
.Pp
.Nm
.Fl e
.Op Fl r
.Op Fl n
.Ar disk
.Pp
This command reads the label from the in-core kernel copy, or directly from the
disk if the
.Fl r
flag is also specified.
The label is written to a file in ASCII and then
supplied to an editor for changes.
If no editor is specified in an
.Ev EDITOR
environment variable,
.Xr vi 1
is used.
When the editor terminates, the label file is used to rewrite the disk label.
Existing bootstrap code is unchanged regardless of whether
.Fl r
was specified.
If
.Fl n
is specified, no data will be written to the device, and instead the
disklabel that would have been written will be printed to stdout.
This is
useful to see how a partitioning scheme will work out for a specific disk.
.Ss Restoring a disk label from a file
To restore a disk label from a file, use the form
.Pp
.Nm
.Fl R
.Op Fl r
.Op Fl n
.Ar disk Ar protofile
.Pp
.Nm
is capable of restoring a disk label that was previously saved in a file
in ASCII format.
The prototype file used to create the label should be in the same format
as that produced when reading or editing a label.
Comments are delimited by
.Ql #
and newline.
As when writing a new label, any existing bootstrap code will be
clobbered if
.Fl r
is specified and will be unaffected otherwise.
See the boot options below for a
method of restoring the label and writing the bootstrap at the same time.
If
.Fl n
is used, no data will be written to the device, and instead the
disklabel that would have been written will be printed to stdout.
This is
useful to see how a partitioning scheme will work out for a specific disk.
.Ss Enabling and disabling writing to the disk label area
By default, it is not possible to write to the disk label area at the beginning
of a disk.
The disk driver arranges for
.Xr write 2
and similar system calls
to return
.Er EROFS
on any attempt to do so.
If you need
to write to this area (for example, to obliterate the label), use the form
.Pp
.Nm
.Fl W
.Ar disk
.Pp
To disallow writing to the label area after previously allowing it,
use the command
.Pp
.Nm
.Fl N
.Ar disk
.Ss Installing bootstraps
The final three forms of
.Nm
are used to install bootstrap code, which allows boot from a
.Xr UFS 5
file system.
If you are creating a
.Dq dangerously-dedicated
slice for compatibility with older PC systems,
you generally want to specify the compatibility slice, such as
.Pa da0s0 .
If you are creating a label within an existing DOS slice,
you should specify
the slice name such as
.Pa da0s1 .
Making a slice bootable can be tricky.
If you are using a normal DOS
slice you typically install (or leave) a standard MBR on the base disk and
then install the
.Dx
bootblocks in the slice.
.Pp
.Nm
.Fl B
.Oo
.Fl b Ar boot1
.Fl s Ar boot2
.Oc
.Ar disk
.Oo Ar disktype Ns / Ns Cm auto Oc
.Pp
This form installs the bootstrap only.
It does not change the disk label.
You should never use this command on the compatibility slice unless you
intend to create a
.Dq dangerously-dedicated
disk, such as
.Ar da0s0 .
This command is typically run on a
.Bx
slice such as
.Ar da0s1 .
.Pp
.Nm
.Fl w
.Fl B
.Op Fl n
.Oo
.Fl b Ar boot1
.Fl s Ar boot2
.Oc
.Ar disk Ar disktype Ns / Ns Cm auto
.Oo Ar packid Oc
.Pp
This form corresponds to the
.Dq write label
command described above.
In addition to writing a new volume label, it also installs the bootstrap.
If run on the compatibility slice this command will create a
.Dq dangerously-dedicated
label.
This command is normally run on a
.Bx
slice rather than the compatibility slice.
If
.Fl n
is used, no data will be written to the device, and instead the
disklabel that would have been written will be printed to stdout.
.Pp
.Nm
.Fl R
.Fl B
.Op Fl n
.Oo
.Fl b Ar boot1
.Fl s Ar boot2
.Oc
.Ar disk Ar protofile
.Oo Ar disktype Ns / Ns Cm auto Oc
.Pp
This form corresponds to the
.Dq restore label
command described above.
In addition to restoring the volume label, it also installs the bootstrap.
If run on the compatibility slice this command will create a
.Dq dangerously-dedicated
label.
This command is normally run on a
.Bx
slice rather than the compatibility
slice.
.Pp
The bootstrap commands always access the disk directly,
so it is not necessary to specify the
.Fl r
flag.
If
.Fl n
is used, no data will be written to the device, and instead the
disklabel that would have been written will be printed to stdout.
.Pp
The bootstrap code is comprised of two boot programs.
Specify the name of the
boot programs to be installed in one of these ways:
.Bl -enum
.It
Specify the names explicitly with the
.Fl b
and
.Fl s
flags.
.Fl b
indicates the primary boot program and
.Fl s
the secondary boot program.
The boot programs are normally located in
.Pa /boot .
.It
If the
.Fl b
and
.Fl s
flags are not specified, but
.Ar disktype
was specified, the names of the programs are taken from the
.Dq b0
and
.Dq b1
parameters of the
.Xr disktab 5
entry for the disk if the disktab entry exists and includes those parameters.
.It
Otherwise, the default boot image names are used:
.Pa /boot/boot1
and
.Pa /boot/boot2
for the standard stage1 and stage2 boot images.
.El
.Ss Initializing/Formatting a bootable disk from scratch
To initialize a disk from scratch the following sequence is recommended.
Please note that this will wipe everything that was previously on the disk,
including any
.No non- Ns Dx
slices.
.Bl -enum
.It
Use
.Xr gpt 8
or
.Xr fdisk 8
to initialize the hard disk, and create a GPT or MBR slice table,
referred to as the
.Dq "partition table"
in
.Tn DOS .
.It
Use
.Nm
or
.Xr disklabel64 8
to define partitions on
.Dx
slices created in the previous step.
.It
Finally use
.Xr newfs_hammer 8
or
.Xr newfs 8
to create file systems on new partitions.
.El
.Pp
A typical partitioning scheme would be to have an
.Ql a
partition
of approximately 512MB to hold the root file system, a
.Ql b
partition for
swap (usually 4GB), a
.Ql d
partition for
.Pa /var
(usually 2GB), an
.Ql e
partition for
.Pa /var/tmp
(usually 2GB), an
.Ql f
partition for
.Pa /usr
(usually around 4GB),
and finally a
.Ql g
partition for
.Pa /home
(usually all remaining space).
If you are tight on space all sizes can be halved.
Your mileage may vary.
.Pp
.Dl "fdisk -BI da0"
.Dl "disklabel32 -w -B da0s1 auto"
.Dl "disklabel32 -e da0s1"
.Ss Manual offset
.Dx
no longer snoop-adjusts the on-disk label when reading or writing
raw labels.
.Nm
is now responsible for adjusting the label when operating in raw mode.
Traditional (32 bit,
.Bx )
disklabels store offsets as absolute block numbers
rather than slice-relative block numbers.
If
.Nm
is unable to issue the
.Dv DIOCGPART
ioctl to get slice information it will
refuse to read or write the label in raw mode.
The
.Fl f
option may be used to force the operation by supplying a manual offset.
.Sh FILES
.Bl -tag -width ".Pa /etc/disktab" -compact
.It Pa /boot/boot1
Default stage1 boot image.
.It Pa /boot/boot2
Default stage2 boot image.
.It Pa /etc/disktab
Disk description file.
.El
.Sh SAVED FILE FORMAT
The
.Nm
utility uses an
.Tn ASCII
version of the label when examining, editing, or restoring a disk label.
The format is:
.Bd -literal -offset 4n
# /dev/ad4s4:
type: unknown
disk: amnesiac
label: fictitious
flags:
bytes/sector: 512
sectors/track: 63
tracks/cylinder: 24
sectors/cylinder: 1512
cylinders: 161098
sectors/unit: 243581184
rpm: 3600
interleave: 1
trackskew: 0
cylinderskew: 0
headswitch: 0		# milliseconds
track-to-track seek: 0	# milliseconds
drivedata: 0

16 partitions:
#          size     offset    fstype
  a:    1048560         16    4.2BSD	#     511.992MB
  b:    8388608    1048576      swap	#    4096.000MB
  c:  243581184          0    unused	#  118936.125MB
  d:    4194304    9437184    4.2BSD	#    2048.000MB
  e:    4194304   13631488    4.2BSD	#    2048.000MB
  f:    8388608   17825792    4.2BSD	#    4096.000MB
  h:  196395264   26214400    HAMMER	#   95896.125MB
  i:   10485760  222609664       ccd	#    5120.000MB
  j:   10485760  233095424     vinum	#    5120.000MB
.Ed
.Pp
Lines starting with a
.Ql #
mark are comments.
Most of the other specifications are no longer used.
The ones which must still be set correctly are:
.Bl -inset
.It Ar label
is an optional label, set by the
.Ar packid
option when writing a label.
.It Ar flags
may be
.Cm removable , ecc
or
.Cm badsect .
.Cm removable
is set for removable media drives, but no current
.Dx
driver evaluates this
flag.
.Cm ecc
is no longer supported;
.Cm badsect
specifies that the drive can perform bad sector remapping.
.It Ar sectors/unit
describes the total size of the disk.
This value must be correct.
.It Ar "the partition table"
is the
.Ux
partition table, not the
.Tn DOS
partition table described in
.Xr fdisk 8 .
.El
.Pp
The partition table can have up to 16 entries.
It contains the following information:
.Bl -tag -width indent
.It Ar #
The partition identifier is a single letter in the range
.Ql a
to
.Ql p .
By convention, partition
.Ql c
is reserved to describe the entire disk.
.It Ar size
The size of the partition in sectors,
.Cm K
(kilobytes - 1024),
.Cm M
(megabytes - 1024*1024),
.Cm G
(gigabytes - 1024*1024*1024),
.Cm T
(gigabytes - 1024*1024*1024*1024),
.Cm %
(percentage of free space
.Em after
removing any fixed-size partitions other than partition
.Ql c ) ,
or
.Cm *
(all remaining free space
.Em after
fixed-size and percentage partitions).
For partition
.Ql c ,
a size of
.Cm *
indicates the entire disk.
Lowercase versions of
.Cm K , M , G ,
and
.Cm T
are allowed.
Size and type should be specified without any spaces between them.
.Pp
Example: 2097152, 1G, 1024M and 1048576K are all the same size
(assuming 512-byte sectors).
.It Ar offset
The offset of the start of the partition from the beginning of the
drive in sectors, or
.Cm *
to have
.Nm
calculate the correct offset to use (the end of the previous partition plus
one, ignoring partition
.Ql c .
For partition
.Ql c ,
.Cm *
will be interpreted as an offset of 0.
.It Ar fstype
Describes the purpose of the partition.
The example shows all currently used partition types.
For
.Xr UFS 5
file systems, use type
.Cm 4.2BSD .
For
.Xr HAMMER 5
file systems, use type
.Cm HAMMER .
For
.Xr ccd 4
partitions, use type
.Cm ccd .
For Vinum drives, use type
.Cm vinum .
Other common types are
.Cm swap
and
.Cm unused .
By convention, partition
.Ql c
represents the entire slice and should be of type
.Cm unused ,
though
.Nm
does not enforce this convention.
The
.Nm
utility
also knows about a number of other partition types,
none of which are in current use.
(See
.Dv fstypenames
in
.In sys/dtype.h
for more details).
.El
.Pp
The remainder of the line is a comment and shows the size of
the partition in MB.
.Sh EXAMPLES
.Dl "disklabel32 da0s1"
.Pp
Display the in-core label for the first slice of the
.Pa da0
disk, as obtained via
.Pa /dev/da0s1 .
(If the disk is
.Dq dangerously-dedicated ,
the compatibility slice name should be specified, such as
.Pa da0s0 . )
.Pp
.Dl "disklabel32 da0s1 > savedlabel"
.Pp
Save the in-core label for
.Pa da0s1
into the file
.Pa savedlabel .
This file can be used with the
.Fl R
option to restore the label at a later date.
.Pp
.Dl "disklabel32 -w -r /dev/da0s1 da2212 foo"
.Pp
Create a label for
.Pa da0s1
based on information for
.Dq da2212
found in
.Pa /etc/disktab .
Any existing bootstrap code will be clobbered
and the disk rendered unbootable.
.Pp
.Dl "disklabel32 -e -r da0s1"
.Pp
Read the on-disk label for
.Pa da0s1 ,
edit it, and reinstall in-core as well as on-disk.
Existing bootstrap code is unaffected.
.Pp
.Dl "disklabel32 -e -r -n da0s1"
.Pp
Read the on-disk label for
.Pa da0s1 ,
edit it, and display what the new label would be (in sectors).
It does
.Em not
install the new label either in-core or on-disk.
.Pp
.Dl "disklabel32 -r -w da0s1 auto"
.Pp
Try to auto-detect the required information from
.Pa da0s1 ,
and write a new label to the disk.
Use another
.Nm Fl e
command to edit the
partitioning and file system information.
.Pp
.Dl "disklabel32 -R da0s1 savedlabel"
.Pp
Restore the on-disk and in-core label for
.Pa da0s1
from information in
.Pa savedlabel .
Existing bootstrap code is unaffected.
.Pp
.Dl "disklabel32 -R -n da0s1 label_layout"
.Pp
Display what the label would be for
.Pa da0s1
using the partition layout in
.Pa label_layout .
This is useful for determining how much space would be allotted for various
partitions with a labelling scheme using
.Cm % Ns -based
or
.Cm *
partition sizes.
.Pp
.Dl "disklabel32 -B da0s1"
.Pp
Install a new bootstrap on
.Pa da0s1 .
The boot code comes from
.Pa /boot/boot1
and possibly
.Pa /boot/boot2 .
On-disk and in-core labels are unchanged.
.Pp
.Dl "disklabel32 -w -B /dev/da0s1 -b newboot1 -s newboot2 da2212"
.Pp
Install a new label and bootstrap.
The label is derived from disktab information for
.Dq da2212
and installed both in-core and on-disk.
The bootstrap code comes from the files
.Pa newboot1
and
.Pa newboot2 .
.Pp
.Dl "dd if=/dev/zero of=/dev/da0 bs=512 count=32"
.Dl "fdisk -BI da0"
.Dl "dd if=/dev/zero of=/dev/da0s1 bs=512 count=32"
.Dl "disklabel32 -w -B da0s1 auto"
.Dl "disklabel32 -e da0s1"
.Pp
Completely wipe any prior information on the disk, creating a new bootable
disk with a DOS partition table containing one
.Dq whole-disk
slice.
Then
initialize the slice, then edit it to your needs.
The
.Pa dd
commands are optional, but may be necessary for some BIOSes to properly
recognize the disk.
.Pp
.Dl "disklabel32 -W da0s1"
.Dl "dd if=/dev/zero of=/dev/da0s1 bs=512 count=32"
.Dl "disklabel64 -r -w da0s1 auto"
.Dl "disklabel64 -N da0s1"
.Pp
Completely wipe any prior information on the slice,
changing label format to 64 bit.
The wiping is needed as
.Nm disklabel64
and
.Nm ,
as a safety measure,
won't do any operations if label with other format is already installed.
.Pp
This is an example disklabel that uses some of the new partition size types
such as
.Cm % , M , G ,
and
.Cm * ,
which could be used as a source file for
.Pp
.Dl "disklabel32 -R ad0s1 new_label_file"
.Bd -literal -offset 4n
# /dev/ad0s1:
type: ESDI
disk: ad0s1
label:
flags:
bytes/sector: 512
sectors/track: 63
tracks/cylinder: 16
sectors/cylinder: 1008
cylinders: 40633
sectors/unit: 40959009
rpm: 3600
interleave: 1
trackskew: 0
cylinderskew: 0
headswitch: 0		# milliseconds
track-to-track seek: 0	# milliseconds
drivedata: 0

16 partitions:
#          size     offset    fstype
  a:       400M          0    4.2BSD
  b:         1G          *      swap
  c:          *          *    unused
  e:     204800          *    4.2BSD
  f:         5g          *    4.2BSD
  g:          *          *    4.2BSD
.Ed
.Sh DIAGNOSTICS
The kernel device drivers will not allow the size of a disk partition
to be decreased or the offset of a partition to be changed while it is open.
Some device drivers create a label containing only a single large partition
if a disk is unlabeled; thus, the label must be written to the
.Ql a
partition of the disk while it is open.
This sometimes requires the desired
label to be set in two steps, the first one creating at least one other
partition, and the second setting the label on the new partition while
shrinking the
.Ql a
partition.
.Pp
On some machines the bootstrap code may not fit entirely in the area
allocated for it by some file systems.
As a result, it may not be possible to have file systems on some partitions
of a
.Dq bootable
disk.
When installing bootstrap code,
.Nm
checks for these cases.
If the installed boot code would overlap a partition of type
.Dv FS_UNUSED
it is marked as type
.Dv FS_BOOT .
The
.Xr newfs 8
utility will disallow creation of file systems on
.Dv FS_BOOT
partitions.
Conversely, if a partition has a type other than
.Dv FS_UNUSED
or
.Dv FS_BOOT ,
.Nm
will not install bootstrap code that overlaps it.
.Sh COMPATIBILITY
Due to
.Xr disklabel32 5
storing sector numbers in 32 bit format
.Nm
is restricted to 2TB, using the prevalent sector size of 512B.
.Xr disklabel64 5
labels should be used to partition larger disks.
.Pp
The various
.Bx Ns s
use slightly different versions of
.Bx
disklabels
and are not generally compatible.
The
.Dx
kernel can often use labels from other
.Bx Ns s
for read-only operation.
.Sh SEE ALSO
.Xr dd 1 ,
.Xr ccd 4 ,
.Xr disklabel32 5 ,
.Xr disktab 5 ,
.Xr boot0cfg 8 ,
.Xr diskinfo 8 ,
.Xr disklabel64 8 ,
.Xr fdisk 8 ,
.Xr gpt 8 ,
.Xr newfs 8 ,
.Xr newfs_hammer 8 ,
.Xr vinum 8
.Sh BUGS
For the i386 architecture, the primary bootstrap sector contains
an embedded
.Em fdisk
table.
The
.Nm
utility takes care to not clobber it when installing a bootstrap only
.Pq Fl B ,
or when editing an existing label
.Pq Fl e ,
but it unconditionally writes the primary bootstrap program onto
the disk for
.Fl w
or
.Fl R ,
thus replacing the
.Em fdisk
table by the dummy one in the bootstrap program.
This is only of
concern if the disk is fully dedicated, so that the
.Bx
disklabel
starts at absolute block 0 on the disk.
.Pp
The
.Nm
utility
does not perform all possible error checking.
Warning
.Em is
given if partitions
overlap; if an absolute offset does not match the expected offset; if the
.Ql c
partition does not start at 0 or does not cover the entire slice; if a
partition runs past the end of the device; and a number of other errors; but
no warning is given if space remains unused.