DISKLABEL64(8) BSD System Manager's Manual DISKLABEL64(8)NAMEdisklabel64 — read and write 64 bit disk pack label
SYNOPSISdisklabel64 [-r] disk
disklabel64-w [-r] [-n] disk disktype/auto [packid]
disklabel64-e [-r] [-n] disk
disklabel64-R [-r] [-n] disk protofile
disklabel64 [-NW] disk
disklabel64-B [-b boot1 -s boot2] disk [disktype/auto]
disklabel64-w -B [-n] [-b boot1 -s boot2] disk disktype/auto [packid]
disklabel64-R -B [-n] [-b boot1 -s boot2] disk protofile [disktype/auto]
DESCRIPTION
The disklabel64 utility installs, examines or modifies a 64 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 (dis‐
play), install or edit the label on a disk. In addition, disklabel64 can
install bootstrap code.
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 disklabel64 command access the in-core copy of
the label. To access the raw (on-disk) copy, use the -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
-r is described under each command.
Disk device name
All disklabel64 forms require a disk device name, which should always be
the raw device name representing the disk or slice. DragonFly uses the
following scheme for slice numbering: If the disk doesn't use GPT (typi‐
cally laid out by gpt(8)), but e.g. MBR (typically laid out by fdisk(8)),
then slice 0, e.g. da0s0, represents the entire disk regardless of any
DOS partitioning. Slice 0 is called the compatibility slice, and slice 1
and onward, e.g. da0s1, represents a BSD slice. If the disk does use
GPT, then all slices are BSD slices, slice 0 isn't special, it is just
the first slice on the disk. You do not have to include the /dev/ path
prefix when specifying the device. The disklabel64 utility will automat‐
ically prepend it.
Reading the disk label
To examine the label on a disk drive, use disklabel64 without options:
disklabel64 [-r] disk
disk represents the raw disk in question, and may be in the form da0s1 or
/dev/da0s1. It will display all of the parameters associated with the
drive and its partition layout. Unless the -r flag is given, the ker‐
nel'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 -r flag is given, disklabel64
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 ini‐
tialized or is corrupt.
Writing a standard label
To write a standard label, use the form
disklabel64-w [-r] [-n] disk disktype/auto [packid]
The required arguments to disklabel64 are the drive to be labeled and the
drive type as described in the 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 identi‐
fication string, up to 16 characters long. The pack id must be quoted if
it contains blanks.
If the -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.
If the -r flag is given, the disk sectors containing the label and boot‐
strap will be written directly. A side-effect of this is that any exist‐
ing 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 -r is not specified, the existing label
will be updated via the in-core copy and any bootstrap code will be unaf‐
fected. If the disk does not already have a label, the -r flag must be
used. In either case, the kernel's in-core label is replaced.
For a virgin disk that is not known to disktab(5), disktype can be speci‐
fied as 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 disk itself must be pro‐
vided as the canonical name, i.e. not as a full path name.
For most harddisks, a label based on percentages for most partitions (and
one partition with a size of ‘*’) will produce a reasonable configura‐
tion.
PC-based systems have special requirements in order for the BIOS to prop‐
erly recognize a DragonFly disklabel. Older systems may require what is
known as a “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 fdisk and then create a DragonFly disklabel within that
slice. This is described later on in this page.
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.
Editing an existing disk label
To edit an existing disk label, use the form
disklabel64-e [-r] [-n] disk
This command reads the label from the in-core kernel copy, or directly
from the disk if the -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 EDITOR environment variable, 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 -r was speci‐
fied. If -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.
Restoring a disk label from a file
To restore a disk label from a file, use the form
disklabel64-R [-r] [-n] disk protofile
disklabel64 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 edit‐
ing a label. Comments are delimited by ‘#’ and newline. As when writing
a new label, any existing bootstrap code will be clobbered if -r is spec‐
ified 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 -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.
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 write(2) and similar
system calls to return EROFS on any attempt to do so. If you need to
write to this area (for example, to obliterate the label), use the form
disklabel64-W disk
To disallow writing to the label area after previously allowing it, use
the command
disklabel64-N disk
Installing bootstraps
The final three forms of disklabel64 are used to install bootstrap code,
which allows boot from a HAMMER(5) or UFS(5) file system. If you are
creating a “dangerously-dedicated” slice for compatibility with older PC
systems, you generally want to specify the compatibility slice, such as
da0s0. If you are creating a label within an existing DOS slice, you
should specify the slice name such as 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 DragonFly
bootblocks in the slice.
disklabel64-B [-b boot1 -s boot2] disk [disktype/auto]
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 “dangerously-dedicated” disk, such as
da0s0. This command is typically run on a BSD slice such as da0s1.
disklabel64-w -B [-n] [-b boot1 -s boot2] disk disktype/auto [packid]
This form corresponds to the “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
“dangerously-dedicated” label. This command is normally run on a BSD
slice rather than the compatibility slice. If -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.
disklabel64-R -B [-n] [-b boot1 -s boot2] disk protofile [disktype/auto]
This form corresponds to the “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
“dangerously-dedicated” label. This command is normally run on a BSD
slice rather than the compatibility slice.
The bootstrap commands always access the disk directly, so it is not nec‐
essary to specify the -r flag. If -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.
The bootstrap code is comprised of two boot programs. Specify the name
of the boot programs to be installed in one of these ways:
1. Specify the names explicitly with the -b and -s flags. -b indicates
the primary boot program and -s the secondary boot program. The
boot programs are normally located in /boot.
2. If the -b and -s flags are not specified, but disktype was speci‐
fied, the names of the programs are taken from the “b0” and “b1”
parameters of the disktab(5) entry for the disk if the disktab entry
exists and includes those parameters.
3. Otherwise, the default boot image names are used: /boot/boot1_64 and
/boot/boot2_64 for the standard stage1 and stage2 boot images.
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 non-DragonFly slices.
1. Use gpt(8) or fdisk(8) to initialize the hard disk, and create a GPT
or MBR slice table, referred to as the “partition table” in DOS.
2. Use disklabel64 or disklabel32(8) to define partitions on DragonFly
slices created in the previous step.
3. Finally use newfs_hammer(8) or newfs(8) to create file systems on
new partitions.
A typical partitioning scheme would be to have an ‘a’ partition of
approximately 512MB to hold the root file system, a ‘b’ partition for
swap (usually 4GB), a ‘d’ partition for /var (usually 2GB), an ‘e’ parti‐
tion for /var/tmp (usually 2GB), an ‘f’ partition for /usr (usually
around 4GB), and finally a ‘g’ partition for /home (usually all remaining
space). If you are tight on space all sizes can be halved. Your mileage
may vary.
gpt create da0
gpt add da0
disklabel64-B -r -w da0s0 auto
disklabel64-e da0s0
ALIGNMENT
When a virgin disklabel64 is laid down a DragonFly 2.5 or later kernel
will align the partition start offset relative to the physical drive
instead of relative to the slice start. This overcomes the issue of
fdisk creating a badly aligned slice by default. The kernel will use a
1MiB (1024 * 1024 byte) alignment. The purpose of this alignment is to
match swap and cluster operations against the physical block size of the
underlying device.
Even though nearly all devices still report a logical sector size of 512,
newer hard drives are starting to use larger physical sector sizes and,
in particular, solid state drives (SSDs) use a physical block size of 64K
(SLC) or 128K (MLC). We choose a 1 megabyte alignment to cover our bases
down the road. 64-bit disklabels are not designed to be put on ultra-
tiny storage devices.
It is worth noting that aligning cluster operations is particularly
important for SSDs and doubly so when swapcache(8) is used with a SSD.
Swapcache is able to use large bulk writes which greatly reduces the
degree of write magnification on SSD media and it is possible to get
upwards of 5x more endurance out of the device than the vendor spec sheet
indicates.
FILES
/boot/boot1_64 Default stage1 boot image.
/boot/boot2_64 Default stage2 boot image.
/etc/disktab Disk description file.
SAVED FILE FORMAT
The disklabel64 utility uses an ASCII version of the label when examin‐
ing, editing, or restoring a disk label. The format is:
# /dev/ad4s4:
#
# Informational fields calculated from the above
# All byte equivalent offsets must be aligned
#
# boot space: 32768 bytes
# data space: 121790552 blocks # 118936.09 MB (124713525248 bytes)
#
diskid: 5e3ef4db-4e24-11dd-8318-010e0cd0bad1
label:
boot2 data base: 0x000000001000
partitions data base: 0x000000009000
partitions data stop: 0x001d0981f000
backup label: 0x001d0981f000
total size: 0x001d09820000 # 118936.12 MB
alignment: 4096
display block size: 1024 # for partition display only
16 partitions:
# size offset fstype fsuuid
a: 524288 0 4.2BSD # 512.000MB
b: 4194304 524288 swap # 4096.000MB
d: 2097152 4718592 4.2BSD # 2048.000MB
e: 2097152 6815744 4.2BSD # 2048.000MB
f: 4194304 8912896 4.2BSD # 4096.000MB
g: 4194304 13107200 4.2BSD # 4096.000MB
h: 94003288 17301504 HAMMER # 91800.086MB
i: 5242880 111304792 ccd # 5120.000MB
j: 5242880 116547672 vinum # 5120.000MB
a-stor_uuid: 4370efdb-4e25-11dd-8318-010e0cd0bad1
b-stor_uuid: 4370eff4-4e25-11dd-8318-010e0cd0bad1
d-stor_uuid: 4370f00b-4e25-11dd-8318-010e0cd0bad1
e-stor_uuid: 4370f024-4e25-11dd-8318-010e0cd0bad1
f-stor_uuid: 4370f03a-4e25-11dd-8318-010e0cd0bad1
g-stor_uuid: 4370f053-4e25-11dd-8318-010e0cd0bad1
h-stor_uuid: 4370f06a-4e25-11dd-8318-010e0cd0bad1
i-stor_uuid: 4370f083-4e25-11dd-8318-010e0cd0bad1
j-stor_uuid: 4370f099-4e25-11dd-8318-010e0cd0bad1
Lines starting with a ‘#’ mark are comments. The specifications which
can be changed are:
label is an optional label, set by the packid option when writing a
label.
the partition table is the UNIX partition table, not the DOS partition
table described in fdisk(8).
The partition table can have up to 16 entries. It contains the following
information:
# The partition identifier is a single letter in the range ‘a’ to
‘p’.
size The size of the partition in sectors, K (kilobytes - 1024), M
(megabytes - 1024*1024), G (gigabytes - 1024*1024*1024), % (per‐
centage of free space after removing any fixed-size partitions),
* (all remaining free space after fixed-size and percentage par‐
titions). Lowercase versions of K, M, and G are allowed. Size
and type should be specified without any spaces between them.
Example: 2097152, 1G, 1024M and 1048576K are all the same size
(assuming 512-byte sectors).
offset The offset of the start of the partition from the beginning of
the drive in sectors, or * to have disklabel64 calculate the cor‐
rect offset to use (the end of the previous partition plus one.
fstype Describes the purpose of the partition. The example shows all
currently used partition types. For UFS(5) file systems, use
type 4.2BSD. For HAMMER(5) file systems, use type HAMMER. For
ccd(4) partitions, use type ccd. For Vinum drives, use type
vinum. Other common types are swap and unused. The disklabel64
utility also knows about a number of other partition types, none
of which are in current use. (See fstypenames in <sys/dtype.h>
for more details).
The remainder of the line is a comment and shows the size of the parti‐
tion in MB.
EXAMPLESdisklabel64 da0s1
Display the in-core label for the first slice of the da0 disk, as
obtained via /dev/da0s1. (If the disk is “dangerously-dedicated”, the
compatibility slice name should be specified, such as da0s0.)
disklabel64 da0s1 > savedlabel
Save the in-core label for da0s1 into the file savedlabel. This file can
be used with the -R option to restore the label at a later date.
disklabel64-w -r /dev/da0s1 da2212 foo
Create a label for da0s1 based on information for “da2212” found in
/etc/disktab. Any existing bootstrap code will be clobbered and the disk
rendered unbootable.
disklabel64-e -r da0s1
Read the on-disk label for da0s1, edit it, and reinstall in-core as well
as on-disk. Existing bootstrap code is unaffected.
disklabel64-e -r -n da0s1
Read the on-disk label for da0s1, edit it, and display what the new label
would be (in sectors). It does not install the new label either in-core
or on-disk.
disklabel64-r -w da0s1 auto
Try to auto-detect the required information from da0s1, and write a new
label to the disk. Use another disklabel64-e command to edit the parti‐
tioning information.
disklabel64-R da0s1 savedlabel
Restore the on-disk and in-core label for da0s1 from information in
savedlabel. Existing bootstrap code is unaffected.
disklabel64-R -n da0s1 label_layout
Display what the label would be for da0s1 using the partition layout in
label_layout. This is useful for determining how much space would be
allotted for various partitions with a labelling scheme using %-based or
* partition sizes.
disklabel64-B da0s1
Install a new bootstrap on da0s1. The boot code comes from
/boot/boot1_64 and possibly /boot/boot2_64. On-disk and in-core labels
are unchanged.
disklabel64-w -B /dev/da0s1 -b newboot1 -s newboot2 da2212
Install a new label and bootstrap. The label is derived from disktab
information for “da2212” and installed both in-core and on-disk. The
bootstrap code comes from the files newboot1 and newboot2.
dd if=/dev/zero of=/dev/da0 bs=512 count=32
fdisk -BI da0
dd if=/dev/zero of=/dev/da0s1 bs=512 count=32
disklabel64-w -B da0s1 auto
disklabel64-e da0s1
Completely wipe any prior information on the disk, creating a new
bootable disk with a DOS partition table containing one “whole-disk”
slice. Then initialize the slice, then edit it to your needs. The dd
commands are optional, but may be necessary for some BIOSes to properly
recognize the disk.
disklabel64-W da0s1
dd if=/dev/zero of=/dev/da0s1 bs=512 count=32
disklabel -r -w da0s1 auto
disklabel -N da0s1
Completely wipe any prior information on the slice, changing label format
to 32 bit. The wiping is needed as disklabel and disklabel64, as a
safety measure, won't do any operations if label with other format is
already installed.
This is an example disklabel that uses some of the new partition size
types such as %, M, G, and *, which could be used as a source file for
disklabel64-R ad0s1 new_label_file
# /dev/ad4s4:
#
# Informational fields calculated from the above
# All byte equivalent offsets must be aligned
#
# boot space: 32768 bytes
# data space: 121790552 blocks # 118936.09 MB (124713525248 bytes)
#
diskid: b1db58a3-4e26-11dd-8318-010e0cd0bad1
label:
boot2 data base: 0x000000001000
partitions data base: 0x000000009000
partitions data stop: 0x001d0981f000
backup label: 0x001d0981f000
total size: 0x001d09820000 # 118936.12 MB
alignment: 4096
display block size: 1024 # for partition display only
16 partitions:
# size offset fstype fsuuid
a: 512M 0 4.2BSD
b: 4G * swap
d: 2G * 4.2BSD
e: 2048M * 4.2BSD
f: 4G * 4.2BSD
g: 4G * 4.2BSD
h: * * HAMMER
i: 5g * ccd
j: 5120m * vinum
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 parti‐
tion if a disk is unlabeled; thus, the label must be written to the ‘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 ‘a’ partition.
SEE ALSOdd(1), uuid(3), ccd(4), disklabel64(5), disktab(5), boot0cfg(8),
diskinfo(8), disklabel32(8), fdisk(8), gpt(8), newfs(8), newfs_hammer(8),
vinum(8)BUGS
For the i386 architecture, the primary bootstrap sector contains an
embedded fdisk table. The disklabel64 utility takes care to not clobber
it when installing a bootstrap only (-B), or when editing an existing
label (-e), but it unconditionally writes the primary bootstrap program
onto the disk for -w or -R, thus replacing the fdisk table by the dummy
one in the bootstrap program. This is only of concern if the disk is
fully dedicated, so that the BSD disklabel starts at absolute block 0 on
the disk.
The disklabel64 utility does not perform all possible error checking.
Warning is given if partitions overlap; if an absolute offset does not
match the expected offset; 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.
BSD September 28, 2009 BSD
