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doc: Improve raid-device-mapping documentation.

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* doc/guix.texi (Mapped Devices): Move examples into the mapping defvars.
Add how to load kernel modules for raid.  Add RAID cindex.

Change-Id: If2d3f3c48940d2428b36bdd85d31c8288db35f3b
Signed-off-by: Ludovic Courtès <ludo@gnu.org>
Modified-by: Ludovic Courtès <ludo@gnu.org>
Merges: #6512
This commit is contained in:
Hugo Buddelmeijer
2026-02-17 20:04:06 +01:00
committed by Ludovic Courtès
parent ccce417a6c
commit f333fb810d
1 changed files with 39 additions and 19 deletions
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doc/guix.texi
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@@ -18968,7 +18968,7 @@ RAID devices are obtained by @dfn{assembling} several other devices, such
as hard disks or partitions, into a new one that behaves as one partition.
Mapped devices are declared using the @code{mapped-device} form,
defined as follows; for examples, see below.
defined as follows.
@deftp {Data Type} mapped-device
Objects of this type represent device mappings that will be made when
@@ -19064,23 +19064,6 @@ options, along with @option{--allow-discards}:
@end lisp
@end table
@end defvar
@defvar raid-device-mapping
This defines a RAID device, which is assembled using the @code{mdadm}
command from the package with the same name. It requires a Linux kernel
module for the appropriate RAID level to be loaded, such as @code{raid456}
for RAID-4, RAID-5 or RAID-6, or @code{raid10} for RAID-10.
@end defvar
@cindex LVM, logical volume manager
@defvar lvm-device-mapping
This defines one or more logical volumes for the Linux
@uref{https://www.sourceware.org/lvm2/, Logical Volume Manager (LVM)}.
The volume group is activated by the @command{vgchange} command from the
@code{lvm2} package.
@end defvar
@cindex disk encryption
@cindex LUKS
The following example specifies a mapping from @file{/dev/sda3} to
@@ -19123,6 +19106,23 @@ swap file is encrypted because the entire device is encrypted.
@xref{Swap Space}, or @xref{Preparing for Installation,,Disk
Partitioning}, for an example.
@end defvar
@defvar raid-device-mapping
@cindex RAID
This defines a RAID device, which is assembled using the @code{mdadm}
command from the package with the same name. It requires a Linux kernel
module for the appropriate RAID level to be loaded, such as @code{raid1} for
RAID-1 (mirroring), @code{raid456} for RAID-4, RAID-5 or RAID-6, or
@code{raid10} for RAID-10 (@pxref{Initial RAM Disk}).
For example, RAID-1 (mirroring) support can be added with:
@lisp
(initrd-modules (cons* "raid1" %base-initrd-modules))
@end lisp
A RAID device formed of the partitions @file{/dev/sda1} and @file{/dev/sdb1}
may be declared as follows:
@@ -19137,7 +19137,22 @@ The @file{/dev/md0} device can then be used as the @code{device} of a
@code{file-system} declaration (@pxref{File Systems}).
Note that the RAID level need not be given; it is chosen during the
initial creation and formatting of the RAID device and is determined
automatically later.
automatically later, assuming the correct Linux modules have been loaded.
Not having the right kernel modules loaded might result in an error message
like this at boot:
@example
mdadm: failed to RUN_ARRAY /dev/md0: Invalid argument
@end example
@end defvar
@cindex LVM, logical volume manager
@defvar lvm-device-mapping
This defines one or more logical volumes for the Linux
@uref{https://www.sourceware.org/lvm2/, Logical Volume Manager (LVM)}.
The volume group is activated by the @command{vgchange} command from the
@code{lvm2} package.
LVM logical volumes ``alpha'' and ``beta'' from volume group ``vg0'' can
be declared as follows:
@@ -19152,6 +19167,7 @@ be declared as follows:
Devices @file{/dev/mapper/vg0-alpha} and @file{/dev/mapper/vg0-beta} can
then be used as the @code{device} of a @code{file-system} declaration
(@pxref{File Systems}).
@end defvar
@node Swap Space
@section Swap Space
@@ -47267,6 +47283,10 @@ file system, you would write:
(initrd-modules (cons "megaraid_sas" %base-initrd-modules)))
@end lisp
Other useful kernel modules include those necessary for a
@code{raid-device-mapping}, e.g. @code{raid1}, @code{raid456} and
@code{raid10} (@pxref{Mapped Devices}).
@defvar %base-initrd-modules
This is the list of kernel modules included in the initrd by default.
@end defvar