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31 .\" @(#)disklabel.8 8.2 (Berkeley) 4/19/94
32 .\" $FreeBSD: src/sbin/disklabel/disklabel.8,v 1.15.2.22 2003/04/17 17:56:34 trhodes Exp $
39 .Nd read and write 64 bit disk pack label
48 .Ar disk Ar disktype Ns / Ns Cm auto
71 .Oo Ar disktype Ns / Ns Cm auto Oc
80 .Ar disk Ar disktype Ns / Ns Cm auto
91 .Oo Ar disktype Ns / Ns Cm auto Oc
96 installs, examines or modifies a 64 bit label on a disk drive or pack.
98 the label, it can be used to change the drive identification, the disk
99 partitions on the drive, or to replace a damaged label.
100 There are several forms
101 of the command that read (display), install or edit the label on a disk.
105 can install bootstrap code.
106 .Ss Raw or in-core label
107 The disk label resides close to or at the beginning of each disk slice.
108 For faster access, the kernel maintains a copy in core at all times.
110 default, most forms of the
112 command access the in-core copy of the label.
113 To access the raw (on-disk)
117 This option allows a label to be installed on a disk without kernel
118 support for a label, such as when labels are first installed on a system; it
119 must be used when first installing a label on a disk.
120 The specific effect of
122 is described under each command.
126 forms require a disk device name, which should always be the raw
127 device name representing the disk or slice.
129 uses the following scheme for slice numbering:
130 If the disk doesn't use GPT (typically laid out by
132 but e.g.\& MBR (typically laid out by
136 represents the entire disk regardless of any DOS partitioning.
137 Slice 0 is called the compatibility slice,
138 and slice 1 and onward, e.g.\&
143 If the disk does use GPT, then all slices are
145 slices, slice 0 isn't special, it is just the first slice on the disk.
146 You do not have to include the
148 path prefix when specifying the device.
151 utility will automatically prepend it.
152 .Ss Reading the disk label
153 To examine the label on a disk drive, use
162 represents the raw disk in question, and may be in the form
166 It will display all of the parameters associated with the drive and its
171 the kernel's in-core copy of the label is displayed;
172 if the disk has no label, or the partition types on the disk are incorrect,
173 the kernel may have constructed or modified the label.
178 reads the label from the raw disk and displays it.
179 Both versions are usually
180 identical except in the case where a label has not yet been initialized or
182 .Ss Writing a standard label
183 To write a standard label, use the form
189 .Ar disk Ar disktype Ns / Ns Cm auto
192 The required arguments to
194 are the drive to be labeled and the drive type as described in the
197 The drive parameters and partitions are taken from that file.
199 different disks of the same physical type are to have different partitions, it
200 will be necessary to have separate disktab entries describing each, or to edit
201 the label after installation as described below.
202 The optional argument is a
203 pack identification string, up to 16 characters long.
205 quoted if it contains blanks.
209 flag is given, no data will be written to the device, and instead the
210 disklabel that would have been written will be printed to stdout.
214 flag is given, the disk sectors containing the label and bootstrap
215 will be written directly.
216 A side-effect of this is that any existing bootstrap code will be overwritten
217 and the disk rendered unbootable.
218 See the boot options below for a method of
219 writing the label and the bootstrap at the same time.
223 the existing label will be updated via the in-core copy and any bootstrap
224 code will be unaffected.
225 If the disk does not already have a label, the
228 In either case, the kernel's in-core label is replaced.
230 For a virgin disk that is not known to
235 In this case, the driver is requested to produce a virgin label for the
237 This might or might not be successful, depending on whether the
238 driver for the disk is able to get the required data without reading
239 anything from the disk at all.
240 It will likely succeed for all SCSI
241 disks, most IDE disks, and vnode devices.
242 Writing a label to the
243 disk is the only supported operation, and the
245 itself must be provided as the canonical name, i.e.\& not as a full
248 For most harddisks, a label based on percentages for most partitions (and
249 one partition with a size of
251 will produce a reasonable configuration.
253 PC-based systems have special requirements in order for the BIOS to properly
257 Older systems may require what is known as a
258 .Dq dangerously dedicated
259 disklabel, which creates a fake DOS partition to work around problems older
260 BIOSes have with modern disk geometries.
261 On newer systems you generally want
262 to create a normal DOS partition using
266 disklabel within that slice.
268 later on in this page.
270 Installing a new disklabel does not in of itself allow your system to boot
271 a kernel using that label.
272 You must also install boot blocks, which is
273 described later on in this manual page.
274 .Ss Editing an existing disk label
275 To edit an existing disk label, use the form
283 This command reads the label from the in-core kernel copy, or directly from the
286 flag is also specified.
287 The label is written to a file in ASCII and then
288 supplied to an editor for changes.
289 If no editor is specified in an
291 environment variable,
294 When the editor terminates, the label file is used to rewrite the disk label.
295 Existing bootstrap code is unchanged regardless of whether
300 is specified, no data will be written to the device, and instead the
301 disklabel that would have been written will be printed to stdout.
303 useful to see how a partitioning scheme will work out for a specific disk.
304 .Ss Restoring a disk label from a file
305 To restore a disk label from a file, use the form
311 .Ar disk Ar protofile
314 is capable of restoring a disk label that was previously saved in a file
316 The prototype file used to create the label should be in the same format
317 as that produced when reading or editing a label.
318 Comments are delimited by
321 As when writing a new label, any existing bootstrap code will be
324 is specified and will be unaffected otherwise.
325 See the boot options below for a
326 method of restoring the label and writing the bootstrap at the same time.
329 is used, no data will be written to the device, and instead the
330 disklabel that would have been written will be printed to stdout.
332 useful to see how a partitioning scheme will work out for a specific disk.
333 .Ss Enabling and disabling writing to the disk label area
334 By default, it is not possible to write to the disk label area at the beginning
336 The disk driver arranges for
338 and similar system calls
341 on any attempt to do so.
343 to write to this area (for example, to obliterate the label), use the form
349 To disallow writing to the label area after previously allowing it,
355 .Ss Installing bootstraps
356 The final three forms of
358 are used to install bootstrap code, which allows boot from a
363 If you are creating a
364 .Dq dangerously-dedicated
365 slice for compatibility with older PC systems,
366 you generally want to specify the compatibility slice, such as
368 If you are creating a label within an existing DOS slice,
370 the slice name such as
372 Making a slice bootable can be tricky.
373 If you are using a normal DOS
374 slice you typically install (or leave) a standard MBR on the base disk and
377 bootblocks in the slice.
386 .Oo Ar disktype Ns / Ns Cm auto Oc
388 This form installs the bootstrap only.
389 It does not change the disk label.
390 You should never use this command on the compatibility slice unless you
392 .Dq dangerously-dedicated
395 This command is typically run on a
408 .Ar disk Ar disktype Ns / Ns Cm auto
411 This form corresponds to the
413 command described above.
414 In addition to writing a new volume label, it also installs the bootstrap.
415 If run on the compatibility slice this command will create a
416 .Dq dangerously-dedicated
418 This command is normally run on a
420 slice rather than the compatibility slice.
423 is used, no data will be written to the device, and instead the
424 disklabel that would have been written will be printed to stdout.
434 .Ar disk Ar protofile
435 .Oo Ar disktype Ns / Ns Cm auto Oc
437 This form corresponds to the
439 command described above.
440 In addition to restoring the volume label, it also installs the bootstrap.
441 If run on the compatibility slice this command will create a
442 .Dq dangerously-dedicated
444 This command is normally run on a
446 slice rather than the compatibility
449 The bootstrap commands always access the disk directly,
450 so it is not necessary to specify the
455 is used, no data will be written to the device, and instead the
456 disklabel that would have been written will be printed to stdout.
458 The bootstrap code is comprised of two boot programs.
459 Specify the name of the
460 boot programs to be installed in one of these ways:
463 Specify the names explicitly with the
469 indicates the primary boot program and
471 the secondary boot program.
472 The boot programs are normally located in
479 flags are not specified, but
481 was specified, the names of the programs are taken from the
487 entry for the disk if the disktab entry exists and includes those parameters.
489 Otherwise, the default boot image names are used:
493 for the standard stage1 and stage2 boot images.
495 .Ss Initializing/Formatting a bootable disk from scratch
496 To initialize a disk from scratch the following sequence is recommended.
497 Please note that this will wipe everything that was previously on the disk,
507 to initialize the hard disk, and create a GPT or MBR slice table,
509 .Dq "partition table"
517 to define partitions on
519 slices created in the previous step.
525 to create file systems on new partitions.
528 A typical partitioning scheme would be to have an
531 of approximately 512MB to hold the root file system, a
534 swap (usually 4GB), a
546 (usually around 4GB),
551 (usually all remaining space).
552 If you are tight on space all sizes can be halved.
553 Your mileage may vary.
557 .Dl "disklabel64 -B -r -w da0s0 auto"
558 .Dl "disklabel64 -e da0s0"
560 When a virgin disklabel64 is laid down a
562 or later kernel will align the partition start offset relative to the
563 physical drive instead of relative to the slice start.
564 This overcomes the issue of fdisk creating a badly aligned slice by default.
565 The kernel will use a 1MiB (1024 * 1024 byte) alignment.
566 The purpose of this alignment is to match swap and cluster operations
567 against the physical block size of the underlying device.
569 Even though nearly all devices still report a logical sector size of 512,
570 newer hard drives are starting to use larger physical sector sizes
571 and, in particular, solid state drives (SSDs) use a physical block size
572 of 64K (SLC) or 128K (MLC). We choose a 1 megabyte alignment to cover our
573 bases down the road. 64-bit disklabels are not designed to be put on
574 ultra-tiny storage devices.
576 It is worth noting that aligning cluster operations is particularly
577 important for SSDs and doubly so when
580 Swapcache is able to use large bulk writes which greatly reduces the degree
581 of write magnification on SSD media and it is possible to get upwards of
582 5x more endurance out of the device than the vendor spec sheet indicates.
584 .Bl -tag -width ".Pa /boot/boot2_64" -compact
585 .It Pa /boot/boot1_64
586 Default stage1 boot image.
587 .It Pa /boot/boot2_64
588 Default stage2 boot image.
590 Disk description file.
592 .Sh SAVED FILE FORMAT
597 version of the label when examining, editing, or restoring a disk label.
599 .Bd -literal -offset 4n
602 # Informational fields calculated from the above
603 # All byte equivalent offsets must be aligned
605 # boot space: 32768 bytes
606 # data space: 121790552 blocks # 118936.09 MB (124713525248 bytes)
608 diskid: 5e3ef4db-4e24-11dd-8318-010e0cd0bad1
610 boot2 data base: 0x000000001000
611 partitions data base: 0x000000009000
612 partitions data stop: 0x001d0981f000
613 backup label: 0x001d0981f000
614 total size: 0x001d09820000 # 118936.12 MB
616 display block size: 1024 # for partition display only
619 # size offset fstype fsuuid
620 a: 524288 0 4.2BSD # 512.000MB
621 b: 4194304 524288 swap # 4096.000MB
622 d: 2097152 4718592 4.2BSD # 2048.000MB
623 e: 2097152 6815744 4.2BSD # 2048.000MB
624 f: 4194304 8912896 4.2BSD # 4096.000MB
625 g: 4194304 13107200 4.2BSD # 4096.000MB
626 h: 94003288 17301504 HAMMER # 91800.086MB
627 i: 5242880 111304792 ccd # 5120.000MB
628 j: 5242880 116547672 vinum # 5120.000MB
629 a-stor_uuid: 4370efdb-4e25-11dd-8318-010e0cd0bad1
630 b-stor_uuid: 4370eff4-4e25-11dd-8318-010e0cd0bad1
631 d-stor_uuid: 4370f00b-4e25-11dd-8318-010e0cd0bad1
632 e-stor_uuid: 4370f024-4e25-11dd-8318-010e0cd0bad1
633 f-stor_uuid: 4370f03a-4e25-11dd-8318-010e0cd0bad1
634 g-stor_uuid: 4370f053-4e25-11dd-8318-010e0cd0bad1
635 h-stor_uuid: 4370f06a-4e25-11dd-8318-010e0cd0bad1
636 i-stor_uuid: 4370f083-4e25-11dd-8318-010e0cd0bad1
637 j-stor_uuid: 4370f099-4e25-11dd-8318-010e0cd0bad1
640 Lines starting with a
643 The specifications which can be changed are:
646 is an optional label, set by the
648 option when writing a label.
649 .It Ar "the partition table"
652 partition table, not the
654 partition table described in
658 The partition table can have up to 16 entries.
659 It contains the following information:
660 .Bl -tag -width indent
662 The partition identifier is a single letter in the range
667 The size of the partition in sectors,
671 (megabytes - 1024*1024),
673 (gigabytes - 1024*1024*1024),
675 (terabytes - 1024*1024*1024*1024),
677 (percentage of free space
679 removing any fixed-size partitions),
681 (all remaining free space
683 fixed-size and percentage partitions).
684 Lowercase versions of
689 Size and type should be specified without any spaces between them.
691 Example: 2097152, 1G, 1024M and 1048576K are all the same size
692 (assuming 512-byte sectors).
694 The offset of the start of the partition from the beginning of the
699 calculate the correct offset to use (the end of the previous partition plus
702 Describes the purpose of the partition.
703 The example shows all currently used partition types.
706 file systems, use type
710 file systems, use type
716 For Vinum drives, use type
718 Other common types are
725 also knows about a number of other partition types,
726 none of which are in current use.
734 The remainder of the line is a comment and shows the size of
737 .Dl "disklabel64 da0s1"
739 Display the in-core label for the first slice of the
741 disk, as obtained via
744 .Dq dangerously-dedicated ,
745 the compatibility slice name should be specified, such as
748 .Dl "disklabel64 da0s1 > savedlabel"
750 Save the in-core label for
754 This file can be used with the
756 option to restore the label at a later date.
758 .Dl "disklabel64 -w -r /dev/da0s1 da2212 foo"
762 based on information for
766 Any existing bootstrap code will be clobbered
767 and the disk rendered unbootable.
769 .Dl "disklabel64 -e -r da0s1"
771 Read the on-disk label for
773 edit it, and reinstall in-core as well as on-disk.
774 Existing bootstrap code is unaffected.
776 .Dl "disklabel64 -e -r -n da0s1"
778 Read the on-disk label for
780 edit it, and display what the new label would be (in sectors).
783 install the new label either in-core or on-disk.
785 .Dl "disklabel64 -r -w da0s1 auto"
787 Try to auto-detect the required information from
789 and write a new label to the disk.
792 command to edit the partitioning information.
794 .Dl "disklabel64 -R da0s1 savedlabel"
796 Restore the on-disk and in-core label for
800 Existing bootstrap code is unaffected.
802 .Dl "disklabel64 -R -n da0s1 label_layout"
804 Display what the label would be for
806 using the partition layout in
808 This is useful for determining how much space would be allotted for various
809 partitions with a labelling scheme using
815 .Dl "disklabel64 -B da0s1"
817 Install a new bootstrap on
819 The boot code comes from
823 On-disk and in-core labels are unchanged.
825 .Dl "disklabel64 -w -B /dev/da0s1 -b newboot1 -s newboot2 da2212"
827 Install a new label and bootstrap.
828 The label is derived from disktab information for
830 and installed both in-core and on-disk.
831 The bootstrap code comes from the files
836 .Dl "dd if=/dev/zero of=/dev/da0 bs=512 count=32"
838 .Dl "dd if=/dev/zero of=/dev/da0s1 bs=512 count=32"
839 .Dl "disklabel64 -w -B da0s1 auto"
840 .Dl "disklabel64 -e da0s1"
842 Completely wipe any prior information on the disk, creating a new bootable
843 disk with a DOS partition table containing one
847 initialize the slice, then edit it to your needs.
850 commands are optional, but may be necessary for some BIOSes to properly
853 .Dl "disklabel64 -W da0s1"
854 .Dl "dd if=/dev/zero of=/dev/da0s1 bs=512 count=32"
855 .Dl "disklabel -r -w da0s1 auto"
856 .Dl "disklabel -N da0s1"
858 Completely wipe any prior information on the slice,
859 changing label format to 32 bit.
860 The wiping is needed as
865 won't do any operations if label with other format is already installed.
867 This is an example disklabel that uses some of the new partition size types
872 which could be used as a source file for
874 .Dl "disklabel64 -R ad0s1 new_label_file"
875 .Bd -literal -offset 4n
878 # Informational fields calculated from the above
879 # All byte equivalent offsets must be aligned
881 # boot space: 32768 bytes
882 # data space: 121790552 blocks # 118936.09 MB (124713525248 bytes)
884 diskid: b1db58a3-4e26-11dd-8318-010e0cd0bad1
886 boot2 data base: 0x000000001000
887 partitions data base: 0x000000009000
888 partitions data stop: 0x001d0981f000
889 backup label: 0x001d0981f000
890 total size: 0x001d09820000 # 118936.12 MB
892 display block size: 1024 # for partition display only
895 # size offset fstype fsuuid
907 The kernel device drivers will not allow the size of a disk partition
908 to be decreased or the offset of a partition to be changed while it is open.
909 Some device drivers create a label containing only a single large partition
910 if a disk is unlabeled; thus, the label must be written to the
912 partition of the disk while it is open.
913 This sometimes requires the desired
914 label to be set in two steps, the first one creating at least one other
915 partition, and the second setting the label on the new partition while
937 does not perform all possible error checking.
941 overlap; if an absolute offset does not match the expected offset; if a
942 partition runs past the end of the device; and a number of other errors; but
943 no warning is given if space remains unused.
projects / dragonfly.git / blob