guide to disks and disk partitions in linux

7/27/2019 Guide to Disks and Disk Partitions in Linux

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Guide to disks and disk partitions in Linux

Recommended Reading, Tutorials/Tips | September 18, 2011 12:22 am

This article is an attempt to provide basic information about disk naming and partitionnumbering conventions, in non-technical terms, to those new to Linux. I believe a basic

understanding of all the aspects concerning how a disk is referenced and partitioned will put you

in a better position to troubleshoot installation and disk-related problems.

Basic information about partition tables and the difference between primary and logical

partitions will be covered.

Hard Drive Naming Convention: The first thing you need to know is there is no C drive orE drive in Linux. There are equivalents, but when you come across a reference to a hard drive

in a modern Linux system, you will typically see something like /dev/sda, /dev/sdb, /dev/sdc, etc. The dev is short for device, and in this case, a block storage device. The sd is short for

SCSI mass-storage driver. (SCSI stands for Small Computer System Interface.) For the rest ofthis article, the /dev/ will be dropped, so all references to hard drives and partitions will start

with the last part only.

The first hard drive detected by a Linux system carries the sda label. In numerical terms, it is

hard drive 0 (zero; counting begins from 0, not 1). The second hard drive is sdb, the third drive,

sdc, and so on. In the screenshot below, there are two hard drives sda and sdb, detected by the


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installer.


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This screenshot comes from an i

system.

Partition Tables: A partition tdevice. And there are two standa

Record) and GPT (GUID Partiti

the first standard. GPT came muit comes with two major limitati

1. It does not allow the concalled primary partitions.

2. Disk partitions may not eThe first limitation will be discusecond in this article.

Partitions and Partition Numb

first be subdivided into distinct sMBR partitioning scheme, whic

different types of partitions Pri

will be discussed further down.

stallation process where three hard drives were

able describes the partitions of a hard drive or ards for the layout of the partition table MBR (

n Table). MBR, also know as ms-dos, is what

h later. While MBR is still the most widely usns which led to the development of GPT. They

iguration of more than four main partitions. Th

xceed 2TB

sed in the next section. Nothing more will be w

ering: To install an operating system on a har

torage units. Those storage units are called partiis the default on virtually all Linux distributio

mary, Extended, and Logical. Extended, and Lo

attached to the

ny storageMaster Boot

ou might call

d partition table,are:

se partitions are

ritten about the

d drive, it must

tions. Under thes, there are three

gical partitions


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With MBR, any partition that is

primary partition. And, as statedscreenshot below was taken fro

created. If you observe closely,

sda4. Unlike hard drives, partiti

the primary partitions, is shownAnd that is because as far as the

So if you attempt to create anothtype of error message shown in t

space, even when you know tha

free space is. It will be unusable.

ot explicitly created as an extended or logical

earlier, there can be no more than four primaryan installation process where four primary par

ou will see that the first primary partition is sd

n numbers start from 1, not 0 (zero). Any space

s Free. But while it may be free, it is, howevsystem is concerned, that free space does not ex

er partition using the free space, the installer wihis image. The error message will always say,

t there is space available. And it does not matte

artition, is a

partitions. Theitions were

1 and the last

not allocated to

r, unusable.ist.

ll throw up thenot enough free

how much that


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To get around the four primary p

involved came up with the conceextended partition, it is then pos

Those partitions are called logic

logical partitions that you can cr

single hard drive.

What the concept of extended pa

You can see that there are three

is an extended partition, which

sda6 and sda7). Under an extendusable. So you do not have to all

extended partition.

Being able to create logical parti

operating systems like Windowsother operating systems has usedtaken while setting up a system t

Fedora 15 and Windows 7), thre

That meant there was just one prfree space as an extended partiti

artitions limit of the MBR partition table, the s

pt of an extended partition. By tagging a partitiible to create many more partitions under the e

l partitions, and theoretically, there is no limit t

ate. Note: Only one extended partition may be

rtition brings to the table is illustrated in the scr

rimary partitions (sda1, sda2 and sda3). And th

akes it possible to create more partitions (in thi

ed partition, you can have free space, and that focate all the available free space to the logical p

ions comes in handy when you have to dual-bo

, PC-BSD or even another Linux distribution, eup three primary partitions. In the image beloo dual-boot Windows 7 and Fedora 15 (see ho

Windows 7 partitions already exist on the targ

imary partition to play with. Only by setting upn, was it possible to install the system. What th

art guys

n as antended partition.

o the number of

onfigured on a

enshot below.

e fourth partition

s example, sda5,

ee space is stillartitions of an

ot with other

pecially if that, which wasto dual-boot

t hard drive.

the availableis also shows is


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that Linux can boot from a logic

In the last two screenshots, the e

does not have to be. In this screepartition (sda2), and first logical

partition is the last primary parti

l partition.

tended partitions were the last primary partitio

nshot, for example, the extended partition is thepartition number is still 5 (sda5). So whether a

ion or not, the logical partition number always

s (sda4). But it

second primaryextended

tarts with the


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number 5.

Not all installation programs bro

what to look for, you can tell if o

partition numbers go from 1, the

the most obvious tell-tale sign o

adcast the presence of an extended partition. Bu

ne exists. In the image below, for example, you

n 5, 6 and 7. The presence of partition number

an extended partition. This image, by the way,

t if you know

can see the

and above, is

was taken while


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installing Ubuntu.

GPT: As stated earlier, GPT,scheme maximum of four prim

below, for example, you can see

The most important point to note

r GUID Partition Table, overcomes two limitatary partitions, and the 2TB limit to partition siz

that there are eight partitions, with about 45GB

here is that all eight partitions are primary part

ons of the MBRes. In the image

still available.

tions, as the


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concept of extended and logical

With GPT, there can always be

case with an MBR scheme that h

create new or additional partitiohas been reached. In the image b

artitions, is foreign to GPT.

nallocated space at the end of existing partition

as no extended partition, that unallocated spa

s, unless the maximum number of partitions poelow, for example, there are six partitions and a

s. And unlike the

e can be used to

ssible with GPTsmall


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unallocated space remaining. Th

Currently, Chakra is the only Limay read GPT disk partitioning

slated for release in early Nove

release show that GPT will be thwill be used if there is an existin

disk. You may read feature previ

alpha screenshots for a few scree

installer.

unallocated space may be used to create a ne

ux distribution that is configured to use GPT buide for Chakra to see the steps involved. Fedo

ber 2011, will support GPT. Test installations

e default on standalone installations. In dual-booperating system installed on MBR partitions

ew of Fedora 16 installer and Fedora 16 KDE a

nshots of GPT partitions in Anaconda, the Fed

partition.

default. Youra 16, which is

f the first beta

t setups, MBRon the target

nd GNOME

ra system

guide to disks and disk partitions in linux

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