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