DiskPartitioning < LCFG

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---+!! Disk Partitioning

On EL7 disk partitioning is done using the [[FstabComponent][fstab component]], this supports adding disks at any time, not just during the install.

For Debian/Ubuntu the partition layout can be configured via the fstab component but the actual work is done in the installer using partman, any post-install changes currently have to be done manually.

The Debian installer partman configuration comes from =templates/lcfg_disks.seed.tt= and =templates/custom_recipe.tt= in the [[https://svn.lcfg.org/viewvc/source/trunk/lcfg-install/][lcfg-install]] package.

%TOC%

---++ LVM

On Debian/Ubuntu LVM is enabled by default at install time and, other than =/boot=, the partitions are created as logical volumes. There is currently no support for disabling LVM other than by overriding all the preseed options. 

<verbatim>
d-i partman-auto/method string lvm
</verbatim>

Note that due to this the partition names for a disk in the fstab resources (e.g. =sda1=, =sda2=) generally have little meaning. The ordering of the tags *is* important though. It is expected that grub/efi and =/boot= partitions come at the start of the list before the partitions which can always be LVM volumes.

Any post-install adjustments to the LVM configuration have to be done manually.

---++ GPT

On EL7 the disk will configured to use GPT when the =fstab.label_&lt;tag>=  (e.g. =fstab.label_sda=) resource is set to =gpt=. On Debian/Ubuntu GPT is enabled by default unless overridden through the preseed resources.

<verbatim>
# Using GPT, not sure this is all absolutely necessary
d-i partman-basicfilesystems/choose_label string gpt
d-i partman-basicfilesystems/default_label string gpt
d-i partman-partitioning/choose_label string gpt
d-i partman-partitioning/default_label string gpt
d-i partman/choose_label string gpt
d-i partman/default_label string gpt
</verbatim>

---++ UEFI / Legacy boot

On EL7 the default is legacy boot, UEFI can be enabled by either defining the =USE_UEFI= macro at the top of the LCFG profile or by including the =lcfg/options/boot-uefi.h= header.

On Debian/Ubuntu the default is UEFI boot, legacy can be enabled by either defining the =USE_LEGACY_BOOT= macro at the top of the LCFG profile or by including the =lcfg/options/boot-legacy.h= header.

As well as controlling the boot mechanism this affects the disk layout.

---+++ EL7

On EL7 with UEFI the partition layout begins like:

<verbatim>
 1      524kB   83.9GB  83.9GB  ext4         sda1
 2      83.9GB  84.2GB  287MB   fat32        sda2  boot
</verbatim>

Where the second partition is mounted as =/boot/efi=. With legacy boot the layout begins like:

<verbatim>
 1      524kB   16.8GB  16.8GB  ext4            sda1
 2      16.8GB  16.8GB  4719kB                  sda2  bios_grub
</verbatim>

In each case the first partition is mounted as =/= (root).

---+++ Debian/Ubuntu

On Debian with UEFI the partition layout looks like:

<verbatim>

</verbatim>

With legacy boot the layout looks like this:

<verbatim>
 1      1049kB  4194kB  3146kB                     bios_grub
 2      4194kB  1029MB  1024MB  ext2
 3      1029MB  21.5GB  20.4GB                     lvm
</verbatim>

Where the second partition is mounted as =/boot=, note that it's not strictly required these days as grub2 can now access LVM volumes.

---++ Disk Encryption

The fstab component provides support for configuring dm-crypt via =/etc/crypttab= so that partitions (e.g. =/tmp= and swap) can be encrypted with a random key at boot time. Work on adding support for this in Debian/Ubuntu is ongoing.

---++ Disk Size

For EL7 the sizes of partitions can be specified explicitly or set to =free= and for swap there is =redhat-autoswap=.

For Debian/Ubuntu partman the disk size is configured via 3 parameters - minimum, maximum and priority. These are used to carve up the disk in the "best" way possible according to some algorithm. The =free= option works in a similar way and will use all remaining disk space after the other partitions have been allocated. The =redhat-autoswap= option gives a minimum of 100% RAM and a maximum of 200% RAM.

---++ Preserving Partitions

The LCFG fstab component supports preserving the partition layout and the contents of particular partitions. Although it should be possible we do not yet support this for Debian/Ubuntu installs. In reality given the switch to LVM by default all systems will need to be fully reinstalled so this is not a big issue at this time.

---++ Partition Layout

---+++ Debian/Ubuntu

The partman recipe can be selected by setting the =install.disk_layout= resource. The default is =lcfg= which means the layout will be driven by the LCFG fstab component resources. It may otherwise be set to one of =atomic=, =multi= or =home= which will mean the standard Debian/Ubuntu recipe of that name is used.

By default the LCFG managed layout is similar to =atomic= but it can be changed to something closer to =multi= by defining the =LCFG_DISK_LAYOUT_MULTI= macro at the start of the LCFG profile. Both support an extra "local part" partition (often =/disk/scratch=) in the usual way. See the [[https://svn.lcfg.org/viewvc/lcfg/core/include/lcfg/options/primary-disk-partitions.h?view=markup][primary-disk-partitions.h]] header for full details.

The standard recipes can be found at:

   * https://salsa.debian.org/installer-team/partman-auto/-/tree/master/recipes
   * https://salsa.debian.org/installer-team/partman-auto/-/tree/master/recipes-amd64-efi

---++ Useful Links

   * https://github.com/xobs/debian-installer/blob/master/doc/devel/partman-auto-recipe.txt
   * https://serverfault.com/questions/953322/preseed-automatic-partitioning
   * https://cptyesterday.wordpress.com/2012/06/17/notes-on-using-expert_recipe-in-debianubuntu-preseed-files/

-- %USERSIG{squinney - 2020-04-17}%
Topic revision: r2 - 2020-04-17 - squinney