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[[Category:File systems]]
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''Partitioning'' a hard drive allows one to logically divide the available space into sections that can be accessed independently of one another.
An entire hard drive may be allocated to a single partition, or one may divide the available storage space across multiple partitions. A number of scenarios require creating multiple partitions: dual- or multi-booting, for example, or maintaining a [[swap]] partition. In other cases, partitioning is used as a means of logically separating data, such as creating separate partitions for audio and video files. Common partitioning schemes are discussed in detail below. 
Each partition should be formatted with to a [[File systems|file system type]] before being used.
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== Partition table ==
Partition information is stored in the partition table; today there are two main formats in use: the classic [[Master Boot Record]], and the modern [[GUID Partition Table]].  The latter is an improved version that does away with several limitations that MBR layouts have.
=== Master Boot Record ===
MBR originally only supported up to 4 partitions.  Later on extended and logical partitions were introduced to get around this limitation.
There are three types of partitions:
* Primary
* Extended
** Logical
'''Primary''' partitions can be bootable and are limited to four partitions per disk or RAID volume.  If a partitioning scheme requires more than four partitions, an '''extended''' partition containing '''logical''' partitions is used.  Extended partitions can be thought of as containers for logical partitions.  A hard disk can contain no more than one extended partition.  The extended partition as a primary partition so if the disk has an extended partition, only three additional primary partitions are possible (i.e. three primary partitions and one extended partition).  The number of logical partitions residing in an extended partition is unlimited.  A system that dual boots Windows will require that Windows reside in a primary partition.
See also [[Wikipedia:Master boot record]].
=== GUID Partition Table ===
There is only one type of partition, '''primary''', but GPT based partition doesn't have any limits on the amount of partitions that can be made.
See also [[Wikipedia:GUID Partition Table]].
=== Choosing between GPT and MBR ===
GUID Partition Table (GPT) is an alternative, contemporary, partitioning style; it is intended to replace the old Master Boot Record (MBR) system.  GPT has several advantages over MBR which has quirks back to MS-DOS times.  With the recent developments to the formatting tools ''fdisk'' (MBR) and ''gdisk'' (GPT), it is equally easy to get good dependability and performance for GPT or MBR.
One should consider these to choose between GPT use MBR.
* If using GRUB legacy as the bootloader, one must use MBR.
* To dual-boot with Windows (both 32-bit and 64-bit) using Legacy BIOS, one must use MBR.
* To dual-boot with Windows 64-bit using UEFI install of BIOS, one must use GPT.
* If you are installing on older hardware, especially a laptop, consider choosing MBR because its BIOS might not support GPT.
* If none of the above apply, choose freely between GPT and MBR; since GPT is more modern, it is recommended in this case.
* It is recommended to always use GPT for UEFI boot as some UEFI firmwares do not allow UEFI-MBR boot.
== Partition scheme ==
There are no strict rules for partitioning a hard drive, although one may follow the general guidance given below.  A disk partitioning scheme is determined by various issues such as desired flexibility, speed, security, as well as the limitations imposed by available disk space.  It is essentially personal preference.  If you would like to dual boot PacBSD with some other operating system please see [[Dual booting]].
=== Single root partition ===
This scheme is the simplest and should be enough for most use cases.  It usually makes sense to start by considering a single {{ic|/}} partition and then separate out others based on specific use cases like RAID, encryption, and shared media partition, etc.  If planning on using [[ZFS]] this is the most plausible choice as it allows for creation of different datasets that can act as partitions.
=== Discrete partitions ===
Separating out a path as a partition allows for the choice of a different filesystem and mount options.  In some cases like a media partition, they can also be shared between operating systems.
=== Mount points ===
The following mount points are possible choices for separate partitions, you can make your decision based on actual needs.
{{Note|PacBSD's filesystem hierarchy is a hybrid between [https://wiki.archlinux.org/index.php/Arch_filesystem_hierarchy Arch Filesystem Hierarchy] and [https://www.freebsd.org/doc/handbook/dirstructure.html FreeBSD Filesystem Hierarchy]}}
==== Root partition ====
{{Note|Upon installation, the {{ic|/}} (root) partition must be mounted '''first''': this is because any directories such as {{ic|/boot}} or {{ic|/home}} that have separate partitions will have to be created in the root file system.  The {{ic|/mnt}} directory of the live system will be used to mount the root partition, and consequently all the other partitions will stem from there.  Once the {{ic|/}} partition has been mounted, any remaining partitions may be mounted in any order.  The general procedure is to first create the mount point, and then mount the partition to it.}}
The root directory is the top of the hierarchy, the point where the primary filesystem is mounted and from which all other filesystem stem.  All files and directories appear under the root directory {ic|/}}, even if they are stored on different physical devices.  The contents of the root filesystem must be adequate to boot, restore, recover, and/or repair the system.  Therefore, certain directories under {{ic|/}} are not candidates for separate partitions.
The {{ic|/}} partition or root partition is necessary and it is the most important.  The other partitions can be replaced by it.
==== /boot ====
The {{ic|/boot}} directory contains programs and configuration file used during operating system bootstrap.
==== /home ====
The {{ic|/home}} directory contains user-specific configuration files, caches, application data and media files.
Separating out {{ic|/home}} allows {{ic|/}} to be re-partitioned separately, but note that you can still reinstall PacBSD with {{ic|/home}} untouched even if it is not separate - the other top-level directories just need to be removed, and then pacstarp can be run.
==== /var ====
The {{ic|/var}} directory stores variable data such as spool directories and files, administrative and logging data, {{ic|pacman}}'s cache, etc. It is used, for example, for caching and logging, and hence frequently read or written. Keeping it in a separate partition avoids running out of disk space due to flunky logs, etc.
It exists to make it possible to mount {ic|/usr}} as read-only. Everything that historically went into {{ic|/usr}} that is written to during system operation (as opposed to installation and software maintenance) must reside under {{ic|/var}}.
==== /tmp ====
The {{ic|/tmp}} directory stores temporary files which are usually not preserved across a system reboot. A memory-based file system is often mounted at {{ic|/tmp}}. This can be automated using the tmpmfs-related variables of [http://www.freebsd.org/cgi/man.cgi?query=rc.conf&sektion=5&manpath=freebsd-release-ports rc.conf(5)] or with an entry in {{ic|/etc/fstab}}; refer to [http://www.freebsd.org/cgi/man.cgi?query=mdmfs&sektion=8&manpath=freebsd-release-ports mdmfs(8)] for details.
==== Swap ====
A [[swap]] partition provides memory that can be used as virtual RAM. A [[Swap#Swap file|swap file]] should be considered too, as they don't have any performance overhead compared to a partition but are much easier to resize as needed. A swap partition can ''potentially'' be shared between operating systems, but not if hibernation is used.
== Partitioning tools ==
== Partition alignment ==
Proper partition alignment is essential for optimal performance and longevity. This is due to the [[wikipedia:Block (data storage)|block]] nature of every I/O operation on the hardware level as well as file system level. The key to alignment is partitioning to (at least) the given ''block size'', which depends on the used hardware. If the partitions are not aligned to begin at multiples of the ''block size'', aligning the file system is a pointless exercise because everything is skewed by the start offset of the partition.
=== Hard disk drives ===
Historically, hard drives were addressed by indicating the ''cylinder'', the ''head'', and the ''sector'' at which data was to be read or written (also known as [[wikipedia:Cylinder-head-sector|CHS addressing]]). These represented the radial position (cylinder), the axial position (drive head: platter and side), and the azimuth (sector) of the data respectively. Nowadays, with [[wikipedia:Logical block addressing|logical block addressing]], the entire hard drive is addressed as one continuous stream of data and the term [[wikipedia:Disk sector|sector]] designates the smallest addressable unit.
The standard ''sector size'' is 512B, but modern high-capacity hard drives use greater value, commonly 4KiB. Using values greater than 512B is referred to as the [[Advanced Format]].
=== Solid state drives ===
Solid state drives are based on [[wikipedia:Flash memory|flash memory]], and thus differ significantly from hard drives. While reading remains possible in a random access fashion, erasure (hence rewriting and random writing) is possible only by [[wikipedia:Flash_memory#Block_erasure|whole blocks]]. Additionally, the ''erase block size'' (EBS) are significantly greater than regular ''block size'', for example 128KiB vs. 4KiB, so it is necessary to align to multiples of EBS. [[NVMe]] drives should be aligned to 4KiB.
=== Partitioning tools ===
In the past, proper alignment required manual calculation and intervention when partitioning. Many of the common partition tools now handle partition alignment automatically:
* ''fdisk''
* ''gdisk''
* ''gparted''
== Partitioning Examples ==
{{Note|You can view a list of installed disk(s) with {{ic|geom disk list}} or {{ic|gpart list adaX | less}} for more info.}}
The following example is for the simplest setup for running PacBSD.
The naming scheme for disk drives under PacBSD are: {{ic|ada''X''}} for SATA drives, and {{ic|da''X''}} for IDE/PATA drives, replace ''X'' with the number of your drive.  Partitions (slices) use the {{ic|sX}} naming convention for ''Primary'' and ''Extended'' partitions and {{ic|sXa}} naming for logical partitions these are prefixed by the drive they are on, an example would be {{ic|/dev/ada0s1}} for the  first partition on the first SATA drive in the system and {{ic|/dev/ada0s2b}} for the second logical partition on the second partition of the first SATA drive.
{{Note|This guide will use {{ic|gpart}} to partition the drive as it supports both MBR and GPT.}}
{{warning|Replace ada0 with the correct drive-identifier for your system, failing to do so might irreplaceably destroy your data, or have other unintended consequences.}}
{{stub|Need to add instructions for setting up partitions for ZFS}}
=== MBR Partitioning ===
{{note|The MBR instructions is not fully tested and should be considered invalid.}}
(Optional) If the disk drive that PacBSD is being installed on has a previous geom, it can be removed with the following command
{{warning|The following command will cause loss of all data that was on the disk.}}
{{bc|# gpart destroy -F ada0}}
First the geom needs to be created, the geom contains information about the partition table for the disk.
{{bc|# gpart create -s mbr ada0}}
Then create a BSD-geom, this creates an extended partition on the drive.
{{bc|# gpart add -t freebsd ada0
# gpart create -s BSD ada0s1}}
{{note|If the first command returns a slice other than {{ic|ada0s1}} then make sure to use that otherwise you may find yourself with an unbootable system.}}
First create the root partition, making sure assign enough space to store all data from program files and user data.  Assuming the drive is a 120Gb drive, one may want to go with something like {{ic|<nowiki>Free Space - Swap = root partition</nowiki>}}:
{{note|At this point you should decide if you want to use UFS or ZFS as the root filesystem.  See [[ZFS#Choosing between UFS and ZFS|choosing between UFS and ZFS]] to help decide between the two}}
To create a partition for UFS use:
{{bc|# gpart add -s 118G -t freebsd-ufs ada0s1}}
To create a partition for ZFS use:
{{bc|# gpart add -s 118G -t freebsd-zfs ada0s1}}
Then create a partition for swap:
{{note|This is not needed if planning on using a Swap file or run with no swap at all}}
{{bc|# gpart add -s 2g -t freebsd-swap ada0s1}}
=== GPT Partitioning ===
(Optional) If the disk drive that PacBSD is being installed on has a previous geom, it can be removed with the following command
{{warning|The following command will cause loss of all data that was on the disk.}}
{{bc|# gpart destroy -F ada0}}
First create the geom:
{{bc|# gpart create -s gpt ada0
# gpart add -s 512k -t freebsd-boot ada0}}
First create the root partition, making sure assign enough space to store all data from program files and user data.  Assuming the drive is a 120Gb drive, one may want to go with something like {{ic|<nowiki>Free Space - Swap = root partition</nowiki>}}:
{{note|At this point you should decide if you want to use UFS or ZFS as the root filesystem.  See [[ZFS#Choosing between UFS and ZFS|choosing between UFS and ZFS]] to help decide between the two}}
To create a partition for UFS use:
{{bc|# gpart add -s 118G -t freebsd-ufs ada0}}
To create a partition for ZFS use:
{{bc|# gpart add -s 118G -t freebsd-zfs ada0}}
Then create a partition for swap:
{{note|This is not needed if planning on using a Swap file or run with no swap at all}}
{{bc|# gpart add -s 2g -t freebsd-swap ada0}}
== See also ==
*[[Wikipedia:Disk partitioning]]
*[http://www.novell.com/coolsolutions/feature/19350.html Manually Partitioning Your Hard Drive with fdisk]
*[http://www.thomas-krenn.com/en/wiki/Partition_Alignment Partition Alignment] (with examples)