mirror of https://github.com/tLDP/LDP
611 lines
28 KiB
XML
611 lines
28 KiB
XML
<?xml version='1.0' encoding='utf-8'?>
|
|
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
|
|
"http://www.docbook.org/xml/4.2/docbookx.dtd">
|
|
<article id="Partition-Mass-Storage-Definitions-Naming-HOWTO">
|
|
<articleinfo>
|
|
<author>
|
|
<firstname>Jean-Daniel</firstname>
|
|
<surname>Dodin</surname>
|
|
<affiliation>
|
|
<!-- A valid email is required. You may add a spam blocker, or get a Yahoo/Gmail/etc account. --> <address>
|
|
<email>jdd@dodin.org</email>
|
|
</address>
|
|
</affiliation>
|
|
</author>
|
|
|
|
<title>Partitions-Mass-Storage-Definitions-Naming-HOWTO</title>
|
|
<revhistory>
|
|
<revision>
|
|
<revnumber>V0.1</revnumber>
|
|
<date>2009-05-09</date>
|
|
<authorinitials>jdd</authorinitials>
|
|
</revision>
|
|
|
|
</revhistory>
|
|
</articleinfo>
|
|
|
|
<section>
|
|
<title>Partitions-Mass-Storage-Definitions-Naming-HOWTO</title>
|
|
<para>Copyright (c) 2009 Jean-Daniel Dodin</para>
|
|
</section>
|
|
<section>
|
|
<title>Copyright and Licence</title>
|
|
<para>The copyright of this document is to the author,
|
|
Jean-Daniel Dodin, according to the following licence.</para>
|
|
<screen>
|
|
<![CDATA[ Permission is granted to copy, distribute and/or modify this
|
|
document under the terms of the GNU Free Documentation License,
|
|
Version 1.2 or any later version published by the Free Software
|
|
Foundation; with no Invariant Sections, no Front-Cover Texts and
|
|
no Back-Cover Texts. A copy of the license is included in the
|
|
section entitled "GNU Free Documentation License".]]>
|
|
</screen>
|
|
<para>
|
|
<ulink url='http://wiki.tldp.org/LdpWikiDefaultLicence#GNUFreeDocumentationLicense'>
|
|
GNU Free Documentation License</ulink>
|
|
</para>
|
|
</section>
|
|
<section>
|
|
<title>Mass Storage Involved Here</title>
|
|
<para>Mass storage involved in the present HOWTO are rewritable
|
|
random access ones. Most of them are magnetic rotating disks
|
|
(floppies, Hard Drive) or flash memory (USB key or any kind of
|
|
memory card).</para>
|
|
<para>For example, cdroms and dvds are
|
|
<emphasis role='strong'>not</emphasis>concerned by this HOWTO (
|
|
<ulink url='http://en.wikipedia.org/wiki/Cdrom'>see
|
|
Wikipedia</ulink>). Tapes are not either.</para>
|
|
<para>Mass storage are used by the kernel, so the basic doc can
|
|
be found on
|
|
<ulink url='http://kernel.org/pub/linux/docs/device-list/devices-2.6+.txt'>
|
|
the kernel Web site</ulink></para>
|
|
<para>Reference site should be
|
|
<ulink url='http://www.idema.org'>the International Disk drive
|
|
Equipment and Materials Association</ulink>.
|
|
<emphasis>Should</emphasis>because this Web site is not very
|
|
friendly.</para>
|
|
</section>
|
|
<section>
|
|
<title>Definitions</title>
|
|
<section>
|
|
<title>Warning</title>
|
|
<para>Many definitions about drives are only virtual. That is
|
|
they are used, but the hardware is often quite different from
|
|
the expected description. Usually this have no odd result,
|
|
any mass storage have to be seen as a
|
|
<emphasis>black box</emphasis>.</para>
|
|
</section>
|
|
<section>
|
|
<title>Bytes</title>
|
|
<para>Computers counts with binaries, 1 & 0,
|
|
1111100001110... To be able to read this better, humans uses
|
|
nibbles (4 bits) often shown as Hexadecimal numbers from 0 to
|
|
f (0123456789abcdef). Nibbles are usually grouped by two and
|
|
this gives a byte. The most used memory unit is byte and it's
|
|
multiples, KiB (Kilo Bytes), MiB (Mega Bytes), GiB
|
|
(Gigabytes). The "i" denotes the binary use (0ne Ki is 1024,
|
|
not 1000), the uppercase "B" denotes Bytes, not bits.</para>
|
|
</section>
|
|
<section>
|
|
<title>Sectors</title>
|
|
<para>Sometime, the word
|
|
<emphasis>block</emphasis>is used in place of
|
|
<emphasis>sectors</emphasis>.</para>
|
|
<para>Mass storage devices (at least the ones we are dealing
|
|
with here) store bytes in "Sectors" of 512 Bytes. This is
|
|
uneven, because any sector count have to be divided by two to
|
|
have the KiB number, so most partitonning software accepts
|
|
letters k (KiB), m (MiB), g... as options. Wise ones do not
|
|
make any case difference.</para>
|
|
<para>Sector size is the available byte count. The true
|
|
sector is bigger, as it have to include housekeeping data.
|
|
You don't have to worry about that.</para>
|
|
<para>Notice that as of 03-22-2006, the IDEMA annouced a new
|
|
sector size of 4kiB (4096 Bytes):
|
|
<ulink url='http://www.idema.org/_smartsite/modules/local/data_file/show_file.php?cmd=download&data_file_id=1446' />-
|
|
doc file, can be openned with OpenOffice.org.</para>
|
|
</section>
|
|
<section>
|
|
<title>Heads</title>
|
|
<para>Rotating mass storage devices uses
|
|
<emphasis>heads</emphasis>. True heads are the physical
|
|
electromechanical device that writes and read the magnetic
|
|
track. Drives being made of rotating plates, the plates have
|
|
two sides, so disks can have two head by plate. Having two
|
|
plates (frequent) you have four heads.</para>
|
|
<para>Heads are writing through very complex system, see
|
|
detailed info here:
|
|
<ulink url='http://www.spmtips.com/library/data_storage' />.</para>
|
|
</section>
|
|
<section>
|
|
<title>Tracks</title>
|
|
<para>Plates are rotating. When a head is still, the plate
|
|
rotation and the width of the head are defining a
|
|
track.</para>
|
|
<para>Heads are moving from the external part of the plate to
|
|
the inner part, step by steps. Each step defines a new
|
|
track.</para>
|
|
</section>
|
|
<section>
|
|
<title>Cylinders</title>
|
|
<para>Heads are moving together, all at the same time. They
|
|
may rotate - on they own center, not the plate center, of
|
|
course. They also may have a linear move. You can see an
|
|
example of linear moving head in any cdreader, looking at the
|
|
move of the laser head. Most disks are as shown by this
|
|
wikipedia image
|
|
<ulink url='http://upload.wikimedia.org/wikipedia/commons/thumb/5/5a/Hard_disk_platters_and_head.jpg/200px-Hard_disk_platters_and_head.jpg' />.</para>
|
|
<para>When you think of all the tracks defined by each head
|
|
at the same time, you have a cylinder. So on a rotating
|
|
drive, all the tracks of the same cylinder are read or
|
|
written at the same time. The actual data is spread on all
|
|
the plates. The way the data is actually written is up to the
|
|
drive manufacturer, not the user.</para>
|
|
</section>
|
|
<section>
|
|
<title>Disks</title>
|
|
<para>Small disks are used directly as a hole bunch of
|
|
sectors. Basic programs can access data directly on sectors.
|
|
Many do (like dd or any partitionning programm).</para>
|
|
<para>But we live in a world of extremely high capacity mass
|
|
storage. Terabytes is normal nowaday (2009), when a complete
|
|
Linux system can live on a floppy (1440 bytes). So there is a
|
|
need of making several parts from a mass storage device,
|
|
though the partitions.</para>
|
|
</section>
|
|
<section>
|
|
<title>Partitions</title>
|
|
<para>Partitioning is a means to divide a single drive into
|
|
many logical drives. A partition is a contiguous set of
|
|
sectors. To lessen the heads travel, partitions can be
|
|
"aligned" on the cylinder size, that is use an integer number
|
|
of cylinder. This is not always done, but should as it have
|
|
many other advantages for recovery.</para>
|
|
</section>
|
|
<section>
|
|
<title>Partition Table</title>
|
|
<para>As you can have many partitions, you need to have a
|
|
partition table. This partition table is stored in the very
|
|
beginning of the drive. It's very unlikely that you will have
|
|
to change this table directly writing bytes with an
|
|
hexadecimal editor, so we wont say more on the position of
|
|
the table.</para>
|
|
<para>There are many Operating Systems all around that all
|
|
share similar hardware and as many partition systems. We will
|
|
look only at what one can find in a PC, even if it's not easy
|
|
to define that nowaday. Say, for us, a PC is any computer
|
|
able to run Linux (I know, it's not always true).</para>
|
|
<para>Each of these partition kinds are noted in the table by
|
|
a special flag called "type" ("t" in fdisk). Most known are
|
|
type 83 for Linux partitions and 82 for Linux swap (hex
|
|
numbers).</para>
|
|
<para>Notice that most Operating Systems can share partition
|
|
tables. At least, if a disk is hardware compatible with
|
|
several systems, these systems should be able to see what the
|
|
others have done, not to erase a drive by accident. I can't
|
|
say for sure that its true in the real life.</para>
|
|
</section>
|
|
<section>
|
|
<title>File Systems</title>
|
|
<para>Partitions can be accessed directly as sectors, as any
|
|
part of the disk, but are usually filled with a
|
|
<emphasis role='strong'>file system</emphasis>. File system
|
|
and partitions are related only because a file system is in a
|
|
partition, but that's all. You can have a disk without
|
|
partition but with a file system or have partitions without
|
|
file system (the swap partition beeing the most well known).
|
|
For details on file systems,
|
|
<ulink url='http://en.wikipedia.org/wiki/File_system'>see
|
|
Wikipedia</ulink>.</para>
|
|
<para>In summary, file systems allow storing data in files
|
|
with human readable names and to sort the files in a friendly
|
|
way, for example as directories, subdirectories, text,
|
|
images...</para>
|
|
</section>
|
|
<section>
|
|
<title>Files and Nodes</title>
|
|
<para>Nearly all what you can find on a mass storage
|
|
partition, beside sectors, from an user point of view, is a
|
|
file. But computers are curious geeks and you can treat files
|
|
like disks if you want. Using the "loop" system, default in
|
|
most Linux kernels, one can partition the inside of the file,
|
|
create file systems on it and mount it. This is specially
|
|
handy for experiments.</para>
|
|
<para>Some of these files are
|
|
<emphasis>devices</emphasis>or
|
|
<emphasis>nodes</emphasis>. Partitions are not files and are
|
|
accessed via special nodes we will see later. These nodes are
|
|
not created by touch but by
|
|
<emphasis>mknode</emphasis>. Use with caution. Nodes need a
|
|
type (
|
|
<emphasis>c</emphasis>for "character" or "b" for
|
|
<emphasis>block</emphasis>) and major and minor numbers. For
|
|
what we need, major numbers are disk numbers and minor
|
|
numbers are partition numbers. The list is visible in
|
|
/proc/partitions</para>
|
|
<screen>
|
|
<![CDATA[cat /proc/partitions
|
|
major minor #blocks name
|
|
|
|
8 0 488386584 sda
|
|
8 1 52436128 sda1
|
|
8 2 1 sda2
|
|
8 5 2104483 sda5
|
|
8 6 20972826 sda6
|
|
8 7 52436128 sda7
|
|
8 8 360434308 sda8]]>
|
|
</screen>
|
|
<screen>
|
|
<![CDATA[#mknod b 8 9 /dev/sda9]]>
|
|
</screen>
|
|
<para>Creates a /dev/sda9 node of no nuse, given this don't
|
|
create partition, only the node. In a usual Linux
|
|
distribution, nodes are dynamically created at boot time, so
|
|
nobody should have to do so. However, sometime the automatic
|
|
system fails.</para>
|
|
</section>
|
|
</section>
|
|
<section>
|
|
<title>Drive Naming in Linux</title>
|
|
<para>There is a special nomenclature that linux uses to refer
|
|
to mass storage that must be understood.</para>
|
|
<section>
|
|
<title>Naming Convention</title>
|
|
<para>Linux used to deal with two kind of drives, depending
|
|
of the electronic interface (controller), IDE and SCSI.
|
|
Oldtimers remember the day where cdwriters where acccessed
|
|
through "SCSI emulation". In fact IDE and SCSI use mostly the
|
|
same low level commands and for 2007 up, with the new "SATA"
|
|
interface, the naming was unified and, in new ditributions,
|
|
all the drives have the same naming. For this part, CD or DVD
|
|
readers/writers are seen like Hard Drives.</para>
|
|
<section>
|
|
<title>Old IDE Names</title>
|
|
<para>By convention, IDE drives where given device names
|
|
<filename class="devicefile">/dev/hda</filename>to
|
|
<filename class="devicefile">/dev/hdd</filename>.
|
|
<emphasis>H</emphasis>ard
|
|
<emphasis>D</emphasis>rive
|
|
<emphasis>A</emphasis>(
|
|
<filename class="devicefile">/dev/hda</filename>) is the first drive and
|
|
<emphasis>H</emphasis>ard
|
|
<emphasis>D</emphasis>rive
|
|
<emphasis>C</emphasis>(
|
|
<filename class="devicefile">/dev/hdc</filename>) is the third.</para>
|
|
<para>A typical PC has two IDE controllers, each of which
|
|
can have two drives connected to it. For example,
|
|
<filename class="devicefile">/dev/hda</filename>is the first drive (master) on the
|
|
first IDE controller and
|
|
<filename class="devicefile">/dev/hdd</filename>is the second (slave) drive on the
|
|
second controller (the fourth IDE drive in the
|
|
computer).</para>
|
|
<para>So, typically, a computer with IDE controller can
|
|
accomodate 4 drives: /dev/hda (primary master), /dev/hdb
|
|
(primary slave), /dev/hdc (secondary master), /dev/hdd
|
|
(secondary slave). Some (rare) Mother Boards have more than
|
|
two controllers, some addition cards can also have
|
|
controllers, these are numbered following the alphabet, but
|
|
one have to figure out what real names are given for his
|
|
particular hardware.</para>
|
|
<para>You can have drives where ever you want, it's not
|
|
mandatory to fill the gaps. You may have interest to read
|
|
about what drive/cdrom connect to what place, but it's out
|
|
of this document scope.</para>
|
|
</section>
|
|
<section>
|
|
<title>New Hard Drives Names</title>
|
|
<para>Now all the rotating hard drives uses the same names
|
|
as the old SCSI controllers, that is "s" in place of "h",
|
|
so /dev/sda, and so on. The number of drives depends on the
|
|
number of controllers on the Mother Board or the extended
|
|
boards. Usually 4 are available. What will be the number of
|
|
a drive is up to the controller card and the way it's read
|
|
by the kernel, so difficult to say at first.</para>
|
|
</section>
|
|
<section>
|
|
<title>Flash Drives Names</title>
|
|
<para>Flash drives are usually not connected through IDE or
|
|
SATA interfaces and so don't uses the same names. Several
|
|
interfaces are used with each different names. The kernel
|
|
documentations gives the names.</para>
|
|
</section>
|
|
<section>
|
|
<title>Low level Devices and Extra naming</title>
|
|
<para>You will find in some apps references to lowlevel
|
|
SCSI devices and various naming conventions, for example
|
|
(wodim is the command line cd burner):</para>
|
|
<screen>
|
|
<![CDATA[wodim --scanbus
|
|
scsibus1:
|
|
1,0,0 100) *
|
|
1,1,0 101) 'TSSTcorp' 'CD/DVDW TS-L632D' 'ac00' Removable CD-ROM
|
|
1,2,0 102) *
|
|
1,3,0 103) *
|
|
1,4,0 104) *
|
|
1,5,0 105) *
|
|
1,6,0 106) *
|
|
1,7,0 107) *]]>
|
|
</screen>
|
|
<para>And you may have to use some sort of
|
|
<emphasis>SCSI:1,1,0</emphasis>option to access the CDROM.
|
|
try to avoid using this as much as possible, as it's very
|
|
error prone and should be let to programmers only. I only
|
|
mention it because you can't always avoid it.</para>
|
|
<para>If you do "cat /dev/ | more", you can see:</para>
|
|
<screen>
|
|
<![CDATA[lrwxrwxrwx 1 root root 3 mars 9 07:56 scd0 -> sr0
|
|
(...)
|
|
crw-r----- 1 root disk 21, 0 mars 9 07:56 sg0
|
|
crw-rw----+ 1 root disk 21, 1 mars 9 07:56 sg1]]>
|
|
</screen>
|
|
<para>These scd, sr, sg devices are lowlevel interface
|
|
(notice the "c" for "character"). Try not using them.
|
|
<emphasis>dmesg</emphasis>and
|
|
<emphasis>more /var/log/boot.msg</emphasis>should give you
|
|
the usable sdxx device, like (short summary):</para>
|
|
<screen>
|
|
<![CDATA[<5>sd 0:0:0:0: [sda] 976773168 512-byte hardware sectors: (500GB/465GiB)
|
|
<5>sd 0:0:0:0: [sda] Write Protect is off
|
|
<7>sd 0:0:0:0: [sda] Mode Sense: 00 3a 00 00]]>
|
|
</screen>
|
|
<para>This mean the drive is
|
|
<emphasis>/dev/sda</emphasis>.</para>
|
|
<para>However these files (given by
|
|
<emphasis>dmesg</emphasis>and
|
|
<emphasis>more /var/log/boot.msg</emphasis>) used to be
|
|
easy to read but are no more. Now the kernel starts in
|
|
parallel several drivers, so the messages are mixed, you
|
|
can have</para>
|
|
<screen>
|
|
<![CDATA[<6> sda:<6>USB Universal Host Contr'ller Interface driver v3.0]]>
|
|
</screen>
|
|
<para>This don't mean that your sda drive is an usb one,
|
|
but the usb module was started at the same time as the
|
|
drive one and send it's messages simultaneously. You still
|
|
have a
|
|
<emphasis>/dev/sda</emphasis>drive.</para>
|
|
</section>
|
|
<section>
|
|
<title>New Media Names</title>
|
|
<para>Here the dmesg content for inserting an USB
|
|
key:</para>
|
|
<screen>
|
|
<![CDATA[scsi7 : SCSI emulation for USB Mass Storage devices
|
|
usb 5-3: New USB device found, idVendor=0951, idProduct=160e
|
|
usb 5-3: New USB device strings: Mfr=1, Product=2, SerialNumber=3
|
|
usb 5-3: Product: DataTraveler 2.0
|
|
usb 5-3: Manufacturer: Kingston
|
|
usb 5-3: SerialNumber: 200706200000000059188185
|
|
usb-storage: device found at 9
|
|
usb-storage: waiting for device to settle before scanning
|
|
scsi 7:0:0:0: Direct-Access Kingston DataTraveler 2.0 1.00 PQ: 0 ANSI: 2
|
|
sd 7:0:0:0: [sdb] 3930112 512-byte hardware sectors: (2.01GB/1.87GiB)
|
|
sd 7:0:0:0: [sdb] Write Protect is off
|
|
sd 7:0:0:0: [sdb] Mode Sense: 23 00 00 00
|
|
sd 7:0:0:0: [sdb] Assuming drive cache: write through
|
|
sd 7:0:0:0: [sdb] 3930112 512-byte hardware sectors: (2.01GB/1.87GiB)
|
|
sd 7:0:0:0: [sdb] Write Protect is off
|
|
sd 7:0:0:0: [sdb] Mode Sense: 23 00 00 00
|
|
sd 7:0:0:0: [sdb] Assuming drive cache: write through
|
|
sdb: sdb1
|
|
sd 7:0:0:0: [sdb] Attached SCSI removable disk
|
|
sd 7:0:0:0: Attached scsi generic sg2 type 0
|
|
usb-storage: device scan complete]]>
|
|
</screen>
|
|
<para>You see there all what we where speaking about right
|
|
now! SCSI emulation, scsi, sd and sg names, but also the
|
|
sdb that is most important for us.</para>
|
|
<para>Here are the messages for a high speed SDHC
|
|
card:</para>
|
|
<screen>
|
|
<![CDATA[tifm_core: MMC/SD card detected in socket 0:1
|
|
mmc1: new SDHC card at address d555
|
|
mmcblk0: mmc1:d555 SD04G 3.79GiB
|
|
mmcblk0: p1
|
|
|
|
/dev/mmcblk0p1 on /media/H2SD type vfat (rw,nosuid,nodev,noatime,flush,uid=1000,utf8,shortname=lower)]]>
|
|
</screen>
|
|
<para>When the two cards are probably the same flash memory
|
|
chip, the USB key uses the USB interface and SCSI
|
|
emulation, the SDHC card uses the PCMCIA slot of the
|
|
laptop, with a special device naming (/dev/mmcblk0). The
|
|
use, as far as partitionning is involved is the
|
|
same.</para>
|
|
</section>
|
|
<section>
|
|
<title>Disk ID</title>
|
|
<para>In a world where disks are many and removable, it's
|
|
impossible to track what device is used by what disk. So
|
|
there are now many way of using a disk name. This makes it
|
|
extremely difficult to work with basic tools. These are
|
|
"Disk labels" and "Disk UUID", also "Partition Labels". See
|
|
fstab man page for details.</para>
|
|
</section>
|
|
</section>
|
|
</section>
|
|
<section>
|
|
<title>Partition Naming in Linux</title>
|
|
<section>
|
|
<title>Numbers</title>
|
|
<para>Partition naming is thanksfully simpler than drive one.
|
|
Partitions are simply given a number from 0 up (decimal).
|
|
Sometime a "p" is appended on front of the number:</para>
|
|
<screen>
|
|
<![CDATA[cat /proc/partitions
|
|
major minor #blocks name
|
|
|
|
8 0 488386584 sda
|
|
8 1 52436128 sda1
|
|
8 2 1 sda2
|
|
8 5 2104483 sda5
|
|
8 6 20972826 sda6
|
|
8 7 52436128 sda7
|
|
8 8 360434308 sda8
|
|
179 0 3979776 mmcblk0
|
|
179 1 3975680 mmcblk0p1]]>
|
|
</screen>
|
|
<para>As you see, partition devices are listed in
|
|
/proc/partition. This file... is not a real file but is
|
|
created on the fly. Don't worry, for what we need it's a
|
|
file.</para>
|
|
<para>Notice the "p1" partition name for the SDHC
|
|
card.</para>
|
|
<para>Max number of partitions is 15 for SCSI and all the
|
|
drives using the new SATA driver, 63 for IDE drives (0 is the
|
|
full drive, 0 to 15 is four bits 0 to 64, 6 bits)</para>
|
|
</section>
|
|
<section>
|
|
<title>Meaning of the Numbers</title>
|
|
<para>Not all the numbers have the same meaning. This mess
|
|
come from the PC history. One can divide floppies with
|
|
partitions, but then 4 ones seems sufficient. But then come
|
|
Hard drives :-). So the partitons numbers 1, 2, 3 and 4 are
|
|
<emphasis>primary</emphasis>partitions. One drive can only
|
|
have 4 primaries.</para>
|
|
<para>To go further, we have to use one of these primary as a
|
|
big one and sub-partition this one, so to have
|
|
<emphasis>logical</emphasis>partitions. The big
|
|
<emphasis>extended</emphasis>partition can be any of the
|
|
4.</para>
|
|
<para>So, remember, the primary partitions are inside the
|
|
drive and the logical partitions are inside one of the
|
|
primary, called the
|
|
<emphasis>extended</emphasis>partition.</para>
|
|
<para>Once the logical partitions are created, it's no more
|
|
recommended to write directly to the extended one. Writing to
|
|
an extended partition would erase the logical ones like
|
|
writing directly to a hard drive erase the partitons. Beware,
|
|
|
|
<emphasis role='strong'>it's possible</emphasis>!!</para>
|
|
<para>If, after creating 4 primary partitions, all the disk
|
|
space is not used, the remaining space is lost (unusable), so
|
|
most of the time, create the desired primaries, then at last
|
|
the extended one with all the remaining room.</para>
|
|
<para>It's not necessary to create 4 primaries. You could use
|
|
only one extended (Linux only), but there are some advantages
|
|
of using primaries.</para>
|
|
<para>Primaries being 4, the first logical partition is
|
|
always 5. So any partition with number of five and up is a
|
|
logical one.</para>
|
|
</section>
|
|
</section>
|
|
<section>
|
|
<title>Device Major and Minor Numbers</title>
|
|
<para>The only important thing with a device file are its major
|
|
and minor device numbers, which are shown instead of the file
|
|
size:</para>
|
|
<screen>
|
|
<![CDATA[$ ls -l /dev/hda
|
|
brw-rw---- 1 root disk 8, 0 mars 9 07:56 /dev/sda]]>
|
|
</screen>
|
|
<para>Shows permissions (
|
|
<systemitem>brw-rw----</systemitem>), owner (root), group (disk), major
|
|
device number (8), minor device number (0), date (mars 9 -
|
|
french, no year), hour (07:56) and device name (guess
|
|
:-).</para>
|
|
<para>When accessing a device file, the major number selects
|
|
which device driver is being called to perform the input/output
|
|
operation. This call is being done with the minor number as a
|
|
parameter and it is entirely up to the driver how the minor
|
|
number is being interpreted. The driver documentation usually
|
|
describes how the driver uses minor numbers.</para>
|
|
</section>
|
|
<section>
|
|
<title>Partition Types</title>
|
|
<section>
|
|
<title>Linux Partition Types</title>
|
|
<para>A partition is labeled to host a certain kind of file
|
|
system (not to be confused with a volume label. Such a file
|
|
system could be the linux standard ext3 file system or linux
|
|
swap space, or even foreign file systems like (Microsoft)
|
|
NTFS or (Sun) UFS. There is a numerical code associated with
|
|
each partition type. For example, the code for ext2 is
|
|
<constant>0x83</constant> and linux swap is
|
|
<constant>0x82</constant> (0x mean hexadecimal).</para>
|
|
</section>
|
|
<section>
|
|
<title>Foreign Partition Types</title>
|
|
<para>The partition type codes have been arbitrarily chosen
|
|
(you can't figure out what they should be) and they are
|
|
particular to a given operating system. Therefore, it is
|
|
theoretically possible that if you use two operating systems
|
|
with the same hard drive, the same code might be used to
|
|
designate two different partition types. OS/2 marks its
|
|
partitions with a 0x07 type and so does Windows NT's NTFS.
|
|
MS-DOS allocates several type codes for its various flavors
|
|
of FAT file systems: 0x01, 0x04 and 0x06 are known. DR-DOS
|
|
used 0x81 to indicate protected FAT partitions, creating a
|
|
type clash with Linux/Minix at that time, but neither
|
|
Linux/Minix nor DR-DOS are widely used any more.</para>
|
|
</section>
|
|
<section>
|
|
<title>Swap Partitions</title>
|
|
<para>Every process running on your computer is allocated a
|
|
number of blocks of RAM. These blocks are called pages. The
|
|
set of in-memory pages which will be referenced by the
|
|
processor in the very near future is called a "working set."
|
|
Linux tries to predict these memory accesses (assuming that
|
|
recently used pages will be used again in the near future)
|
|
and keeps these pages in RAM if possible.</para>
|
|
<para>If you have too many processes running on a machine,
|
|
the kernel will try to free up RAM by writing pages to disk.
|
|
This is what swap space is for. It effectively increases the
|
|
amount of memory you have available. However, disk I/O is
|
|
about a hundred times slower than reading from and writing to
|
|
RAM. Consider this emergency memory and not extra
|
|
memory.</para>
|
|
<para>If memory becomes so scarce that the kernel pages out
|
|
from the working set of one process in order to page in for
|
|
another, the machine is said to be thrashing. Some readers
|
|
might have inadvertenly experienced this: the hard drive is
|
|
grinding away like crazy, but the computer is slow to the
|
|
point of being unusable. Swap space is something you need to
|
|
have, but it is no substitute for sufficient RAM.</para>
|
|
</section>
|
|
<section>
|
|
<title>Complete List</title>
|
|
<para>From the fdisk help:</para>
|
|
<screen>
|
|
<![CDATA[ 0 Vide 1e Hidden W95 FAT1 80 Old Minix bf Solaris
|
|
1 FAT12 24 NEC DOS 81 Minix / old Lin c1 DRDOS/sec (FAT-
|
|
2 XENIX root 39 Plan 9 82 Linux swap / So c4 DRDOS/sec (FAT-
|
|
3 XENIX usr 3c PartitionMagic 83 Linux c6 DRDOS/sec (FAT-
|
|
4 FAT16 <32M 40 Venix 80286 84 OS/2 hidden C: c7 Syrinx
|
|
5 Extended 41 PPC PReP Boot 85 Linux extended da Non-FS data
|
|
6 FAT16 42 SFS 86 NTFS volume set db CP/M / CTOS / .
|
|
7 HPFS/NTFS 4d QNX4.x 87 NTFS volume set de Dell Utility
|
|
8 AIX 4e QNX4.x 2nd part 88 Linux plein tex df BootIt
|
|
9 AIX bootable 4f QNX4.x 3rd part 8e Linux LVM e1 DOS access
|
|
a OS/2 Boot Manag 50 OnTrack DM 93 Amoeba e3 DOS R/O
|
|
b W95 FAT32 51 OnTrack DM6 Aux 94 Amoeba BBT e4 SpeedStor
|
|
c W95 FAT32 (LBA) 52 CP/M 9f BSD/OS eb BeOS fs
|
|
e W95 FAT16 (LBA) 53 OnTrack DM6 Aux a0 IBM Thinkpad hi ee GPT
|
|
f W95 Etendu (LBA 54 OnTrackDM6 a5 FreeBSD ef EFI (FAT-12/16/
|
|
10 OPUS 55 EZ-Drive a6 OpenBSD f0 Linux/PA-RISC b
|
|
11 Hidden FAT12 56 Golden Bow a7 NeXTSTEP f1 SpeedStor
|
|
12 Compaq diagnost 5c Priam Edisk a8 UFS Darwin f4 SpeedStor
|
|
14 Hidden FAT16 <3 61 SpeedStor a9 NetBSD f2 DOS secondary
|
|
16 Hidden FAT16 63 GNU HURD or Sys ab Amorce Darwin fb VMware VMFS
|
|
17 Hidden HPFS/NTF 64 Novell Netware b7 BSDI fs fc VMware VMKCORE
|
|
18 AST SmartSleep 65 Novell Netware b8 BSDI swap fd Linux raid auto
|
|
1b Hidden W95 FAT3 70 DiskSecure Mult bb Boot Wizard hid fe LANstep
|
|
1c Hidden W95 FAT3 75 PC/IX be Amorce Solaris ff BBT]]>
|
|
</screen>
|
|
</section>
|
|
</section>
|
|
<section>
|
|
<title>How Many Partitions</title>
|
|
<para>The exact number of partitions allowed on a drive is
|
|
fixed by the kernel. So you can find the exact number is the
|
|
kernel documentation, the last version is maintained here
|
|
<ulink url='http://kernel.org/pub/linux/docs/device-list/' />If
|
|
you have the kernel source installed, you can find your version
|
|
on your computer at
|
|
/usr/src/linux/Documentation/devices.txt.</para>
|
|
<para>Look at "limit on partition". Find yours. Common SATA
|
|
number is 31, SCSI is 15, some are less.</para>
|
|
</section>
|
|
</article>
|
|
|
|
|