en/handbook/hb-install-alpha-disk.xml

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<sections>

<version>1.10</version>
<date>2004-12-30</date>

<section>
<title>Introduction to Block Devices</title>
<subsection>
<title>Block Devices</title>
<body>

<p>
We'll take a good look at disk-oriented aspects of Gentoo Linux
and Linux in general, including Linux filesystems, partitions and block devices.
Then, once you're familiar with the ins and outs of disks and filesystems,
you'll be guided through the process of setting up partitions and filesystems
for your Gentoo Linux installation.
</p>

<p>
To begin, we'll introduce <e>block devices</e>. The most famous block device is
probably the one that represents the first SCSI HD in a Linux system, namely
<path>/dev/sda</path>.
</p>

<p>
The block devices above represent an abstract interface to the disk. User
programs can use these block devices to interact with your disk without worrying
about whether your drives are IDE, SCSI or something else. The program can
simply address the storage on the disk as a bunch of contiguous,
randomly-accessible 512-byte blocks.
</p>

</body>
</subsection>
<subsection>
<title>Slices</title>
<body>

<p>
Although it is theoretically possible to use a full disk to house your Linux
system, this is almost never done in practice. Instead, full disk block devices
are split up in smaller, more manageable block devices. On Alpha systems,
these are called <e>slices</e>. 
</p>

</body>
</subsection>
</section>
<section>
<title>Designing a Partitioning Scheme</title>
<subsection>
<title>Default Partitioning Scheme</title>
<body>

<p>
As an example we use the following slice layout:
</p>

<table>
<tr>
  <th>Slice</th>
  <th>Description</th>
</tr>
<tr>
  <ti><path>/dev/sda1</path></ti>
  <ti>Swap slice</ti>
</tr>
<tr>
  <ti><path>/dev/sda2</path></ti>
  <ti>Root slice</ti>
</tr>
<tr>
  <ti><path>/dev/sda3</path></ti>
  <ti>Full disk (required)</ti>
</tr>
</table>


<p>
If you are interested in knowing how big a partition should be, or even how 
many partitions (or volumes) you need, read on. Otherwise continue now with
<uri link="#fdisk">Using fdisk to Partition your Disk</uri>.
</p>

</body>
</subsection>
<subsection>
<title>How Many and How Big?</title>
<body>

<p>
The number of partitions is highly dependent on your environment. For instance,
if you have lots of users, you will most likely want to have your
<path>/home</path> separate as it increases security and makes backups easier.
If you are installing Gentoo to perform as a mailserver, your 
<path>/var</path> should be separate as all mails are stored inside 
<path>/var</path>. A good choice of filesystem will then maximise your 
performance. Gameservers will have a separate <path>/opt</path> as most gaming 
servers are installed there. The reason is similar for <path>/home</path>: 
security and backups.
</p>

<p>
As you can see, it very much depends on what you want to achieve. Separate
partitions or volumes have the following advantages:
</p>

<ul>
<li>
  You can choose the best performing filesystem for each partition or volume
</li>
<li>
  Your entire system cannot run out of free space if one defunct tool is
  continuously writing files to a partition or volume
</li>
<li>
  If necessary, file system checks are reduced in time, as multiple checks can
  be done in parallel (although this advantage is more with multiple disks than
  it is with multiple partitions)
</li>
<li>
  Security can be enhanced by mounting some partitions or volumes read-only, 
  nosuid (setuid bits are ignored), noexec (executable bits are ignored) etc.
</li>
</ul>

<p>
However, multiple partitions have one big disadvantage: if not configured 
properly, you might result in having a system with lots
of free space on one partition and none on another.
</p>

</body>
</subsection>
</section>
<section id="fdisk">
<title>Using fdisk to Partition your Disk (SRM only)</title>
<subsection>
<body>

<p>
The following parts explain how to create the example slice layout described
previously, namely:
</p>

<table>
<tr>
  <th>Slice</th>
  <th>Description</th>
</tr>
<tr>
  <ti><path>/dev/sda1</path></ti>
  <ti>Swap slice</ti>
</tr>
<tr>
  <ti><path>/dev/sda2</path></ti>
  <ti>Root slice</ti>
</tr>
<tr>
  <ti><path>/dev/sda3</path></ti>
  <ti>Full disk (required)</ti>
</tr>
</table>

<p>
Change your slice layout according to your own preference.
</p>


</body>
</subsection>
<subsection>
<title>Identifying Available Disks</title>
<body>

<p>
To figure out what disks you have running, use the following commands:
</p>

<pre caption="Identifying available disks">
# <i>dmesg | grep 'drive$'</i>        <comment>(For IDE disks)</comment>
# <i>dmesg | grep 'scsi'</i>          <comment>(For SCSI disks)</comment>
</pre>

<p>
From this output you should be able to see what disks were detected and their
respective <path>/dev</path> entry. In the following parts we assume that the
disk is a SCSI disk on <path>/dev/sda</path>.
</p>

<p>
Now fire up <c>fdisk</c>:
</p>

<pre caption="Starting fdisk">
# <i>fdisk /dev/sda</i>
</pre>

</body>
</subsection>
<subsection>
<title>Deleting All Slices</title>
<body>

<p>
If your hard drive is completely blank, then you'll have to first create 
a BSD disklabel.
</p>

<pre caption="Creating a BSD disklabel">
Command (m for help): <i>b</i>
/dev/sda contains no disklabel.
Do you want to create a disklabel? (y/n) <i>y</i>
<comment>A bunch of drive-specific info will show here</comment>
3 partitions:
#       start       end      size     fstype   [fsize bsize   cpg]                                    
  c:        1      5290*     5289*    unused        0     0
</pre>

<p>
We start with deleting all slices <e>except</e> the 'c'-slice (a requirement 
for using BSD disklabels).  The following shows how to delete a slice (in 
the example we use 'a').  Repeat the process to delete all other slices 
(again, except the 'c'-slice).
</p>

<p>
Use <c>p</c> to view all existing slices. <c>d</c> is used to delete a slice.
</p>

<pre caption="Deleting a slice">
BSD disklabel command (m for help): <i>p</i>

8 partitions:
#       start       end      size     fstype   [fsize bsize   cpg]                                    
  a:        1       235*      234*    4.2BSD     1024  8192    16
  b:      235*      469*      234*      swap
  c:        1      5290*     5289*    unused        0     0
  d:      469*     2076*     1607*    unused        0     0
  e:     2076*     3683*     1607*    unused        0     0
  f:     3683*     5290*     1607*    unused        0     0
  g:      469*     1749*     1280     4.2BSD     1024  8192    16
  h:     1749*     5290*     3541*    unused        0     0

BSD disklabel command (m for help): <i>d</i>
Partition (a-h): <i>a</i>
</pre>

<p>
After repeating this process for all slices, a listing should show you something
similar to this:
</p>

<pre caption="Viewing an empty scheme">
BSD disklabel command (m for help): <i>p</i>

3 partitions:
#       start       end      size     fstype   [fsize bsize   cpg]                                    
  c:        1      5290*     5289*    unused        0     0
</pre>

</body>
</subsection>
<subsection>
<title>Creating the Swap Slice</title>
<body>

<p>
On Alpha based systems you don't need a separate boot partition. However, the
first cylinder cannot be used as the <c>aboot</c> image will be placed there.
</p>

<p>
We will create a swap slice starting at the third cylinder, with a total
size of 1 Gbyte. Use <c>n</c> to create a new slice. After creating the slice,
we will change its type to <c>1</c> (one), meaning <e>swap</e>.
</p>

<pre caption="Creating the swap slice">
BSD disklabel command (m for help): <i>n</i>
Partition (a-p): <i>a</i>
First cylinder (1-5290, default 1): <i>3</i>
Last cylinder or +size or +sizeM or +sizeK (3-5290, default 5290): <i>+1024M</i>

BSD disklabel command (m for help): <i>t</i>
Partition (a-c): <i>a</i>
Hex code (type L to list codes): <i>1</i>
</pre>

<p>
After these steps you should see a layout similar to the following:
</p>

<pre caption="Slice layout after creating the swap slice">
BSD disklabel command (m for help): <i>p</i>

3 partitions:
#       start       end      size     fstype   [fsize bsize   cpg]                                    
  a:        3      1003      1001       swap
  c:        1      5290*     5289*    unused        0     0
</pre>

</body>
</subsection>
<subsection>
<title>Create the Root Slice</title>
<body>

<p>
We will now create the root slice, starting from the first cylinder <e>after</e>
the swap slice. Use the <c>p</c> command to view where the swap slice ends. In
our example, this is at 1003, making the root partition start at 1004.
</p>

<p>
Another problem is that there is currently a bug in <c>fdisk</c> making it think
the number of available cylinders is one above the real number of cylinders. In
other words, when you are asked for the last cylinder, decrease the cylinder
number (in this example: 5290) with one.
</p>

<p>
When the partition is created, we change the type to <c>8</c>, for <e>ext2</e>.
</p>

<pre caption="Creating the root slice">
D disklabel command (m for help): <i>n</i>
Partition (a-p): <i>b</i>
First cylinder (1-5290, default 1): <i>1004</i>
Last cylinder or +size or +sizeM or +sizeK (1004-5290, default 5290): <i>5289</i>

BSD disklabel command (m for help): <i>t</i>
Partition (a-c): <i>b</i>
Hex code (type L to list codes): <i>8</i>
</pre>

<p>
Your slice layout should now be similar to this:
</p>

<pre caption="Viewing the slice layout">
BSD disklabel command (m for help): <i>p</i>

3 partitions:
#       start       end      size     fstype   [fsize bsize   cpg]                                    
  a:        3      1003      1001       swap
  b:     1004      5289      4286       ext2
  c:        1      5290*     5289*    unused        0     0
</pre>

</body>
</subsection>
<subsection>
<title>Save the Slice Layout and Exit</title>
<body>

<p>
Save <c>fdisk</c> by typing <c>w</c>. This will also save your slice layout.
</p>

<pre caption="Save and exit fdisk">
Command (m for help): <i>w</i>
</pre>

<p>
Now that your slices are created, you can now continue with <uri
link="#filesystems">Creating Filesystems</uri>.
</p>

</body>
</subsection>
</section>
<section id="fdisk">
<title>Using fdisk to Partition your Disk (ARC/AlphaBIOS only)</title>
<subsection>
<body>

<p>
The following parts explain how to partition the disk with a layout 
similar to the one described previously, namely:
</p>

<table>
<tr>
  <th>Partition</th>
  <th>Description</th>
</tr>
<tr>
  <ti><path>/dev/sda1</path></ti>
  <ti>Boot partition</ti>
</tr>
<tr>
  <ti><path>/dev/sda2</path></ti>
  <ti>Swap partition</ti>
</tr>
<tr>
  <ti><path>/dev/sda3</path></ti>
  <ti>Root partition</ti>
</tr>
</table>

<p>
Change your partition layout according to your own preference.
</p>

</body>
</subsection>
<subsection>
<title>Identifying Available Disks</title>
<body>

<p>
To figure out what disks you have running, use the following commands:
</p>

<pre caption="Identifying available disks">
# <i>dmesg | grep 'drive$'</i>        <comment>(For IDE disks)</comment>
# <i>dmesg | grep 'scsi'</i>          <comment>(For SCSI disks)</comment>
</pre>

<p>
From this output you should be able to see what disks were detected and their
respective <path>/dev</path> entry. In the following parts we assume that the
disk is a SCSI disk on <path>/dev/sda</path>.
</p>

<p>
Now fire up <c>fdisk</c>:
</p>

<pre caption="Starting fdisk">
# <i>fdisk /dev/sda</i>
</pre>

</body>
</subsection>
<subsection>
<title>Deleting All Partitions</title>
<body>

<p>
If your hard drive is completely blank, then you'll have to first create 
a DOS disklabel.
</p>

<pre caption="Creating a DOS disklabel">
Command (m for help): <i>o</i>
Building a new DOS disklabel.
</pre>

<p>
We start with deleting all partitions.  The following shows how to delete 
a partition (in the example we use '1').  Repeat the process to delete all 
other partitions.
</p>

<p>
Use <c>p</c> to view all existing partitions.  <c>d</c> is used to delete a
partition.
</p>

<pre caption="Deleting a partition">
command (m for help): <i>p</i>

Disk /dev/sda: 9150 MB, 9150996480 bytes
64 heads, 32 sectors/track, 8727 cylinders
Units = cylinders of 2048 * 512 = 1048576 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1         478      489456   83  Linux
/dev/sda2             479        8727     8446976    5  Extended
/dev/sda5             479        1433      977904   83  Linux Swap
/dev/sda6            1434        8727     7469040   83  Linux

command (m for help): <i>d</i>
Partition number (1-6): <i>1</i>
</pre>


</body>
</subsection>
<subsection>
<title>Creating the Boot Partition</title>
<body>

<p>
On Alpha systems which use MILO to boot, we have to create a small vfat 
boot partition.
</p>

<pre caption="Creating the boot partition">
Command (m for help): <i>n</i>
Command action
  e   extended
  p   primary partition (1-4)
<i>p</i>
Partition number (1-4): <i>1</i>
First cylinder (1-8727, default 1): <i>1</i>
Last cylinder or +size or +sizeM or +sizeK (1-8727, default 8727): <i>+16M</i>

Command (m for help): <i>t</i>
Selected partition 1
Hex code (type L to list codes): <i>6</i>
Changed system type of partition 1 to 6 (FAT16)
</pre>

</body>
</subsection>
<subsection>
<title>Creating the Swap Partition</title>
<body>

<p>
We will create a swap partition starting at the third cylinder, with a total
size of 1 Gbyte.  Use <c>n</c> to create a new partition.
</p>

<pre caption="Creating the swap partition">
Command (m for help): <i>n</i>
Command action
  e   extended
  p   primary partition (1-4)
<i>p</i>
Partition number (1-4): <i>2</i>
First cylinder (17-8727, default 17): <i>17</i>
Last cylinder or +size or +sizeM or +sizeK (17-8727, default 8727): <i>+1000M</i>

Command (m for help): <i>t</i>
Partition number (1-4): <i>1</i>
Hex code (type L to list codes): <i>82</i>
Changed system type of partition 2 to 82 (Linux swap)
</pre>

<p>
After these steps you should see a layout similar to the following:
</p>

<pre caption="Partition listing after creating a swap partition">
Command (m for help): <i>p</i>

Disk /dev/sda: 9150 MB, 9150996480 bytes
64 heads, 32 sectors/track, 8727 cylinders
Units = cylinders of 2048 * 512 = 1048576 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1          16       16368    6  FAT16
/dev/sda2              17         971      977920   82  Linux swap
</pre>

</body>
</subsection>
<subsection>
<title>Creating the Root Partition</title>
<body>

<p>
We will now create the root partition.  Again, just use the <c>n</c> command.
</p>

<pre caption="Creating the root partition">
Command (m for help): <i>n</i>
Command action
  e   extended
  p   primary partition (1-4)
<i>p</i>
Partition number (1-4): <i>3</i>
First cylinder (972-8727, default 972): <i>972</i>
Last cylinder or +size or +sizeM or +sizeK (972-8727, default 8727): <i>8727</i>
</pre>

<p>
After these steps you should see a layout similar to the following:
</p>

<pre caption="Partition listing after creating the root partition">
Command (m for help): <i>p</i>

Disk /dev/sda: 9150 MB, 9150996480 bytes
64 heads, 32 sectors/track, 8727 cylinders
Units = cylinders of 2048 * 512 = 1048576 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1          16       16368    6  FAT16
/dev/sda2              17         971      977920   82  Linux swap
/dev/sda3             972        8727     7942144   83  Linux
</pre>

</body>
</subsection>
<subsection>
<title>Save the Partition Layout and Exit</title>
<body>

<p>
Save <c>fdisk</c> by typing <c>w</c>. This will also save your partition layout.
</p>

<pre caption="Save and exit fdisk">
Command (m for help): <i>w</i>
</pre>

<p>
Now that your partitions are created, you can now continue with <uri
link="#filesystems">Creating Filesystems</uri>.
</p>

</body>
</subsection>
</section>
<section id="filesystems">
<title>Creating Filesystems</title>
<subsection>
<title>Introduction</title>
<body>

<p>
Now that your partitions are created, it is time to place a filesystem on them. 
If you don't care about what filesystem to choose and are happy with what we use
as default in this handbook, continue with <uri 
link="#filesystems-apply">Applying a Filesystem to a Partition</uri>.
Otherwise read on to learn about the available filesystems...
</p>

</body>
</subsection>
<subsection>
<title>Filesystems?</title>
<body>

<p>
Several filesystems are available. Most of them are found stable on the
Alpha architecture.
</p>

<p>
<b>ext2</b> is the tried and true Linux filesystem but doesn't have metadata
journaling, which means that routine ext2 filesystem checks at startup time can
be quite time-consuming. There is now quite a selection of newer-generation
journaled filesystems that can be checked for consistency very quickly and are
thus generally preferred over their non-journaled counterparts. Journaled
filesystems prevent long delays when you boot your system and your filesystem
happens to be in an inconsistent state.
</p>

<p>
<b>ext3</b> is the journaled version of the ext2 filesystem, providing metadata
journaling for fast recovery in addition to other enhanced journaling modes like
full data and ordered data journaling. ext3 is a very good and reliable
filesystem. It has an additional hashed b-tree indexing option that enables 
high performance in almost all situations. In short, ext3 is an excellent 
filesystem.
</p>

<p>
<b>ReiserFS</b> is a B*-tree based filesystem that has very good overall 
performance and greatly outperforms both ext2 and ext3 when dealing with small 
files (files less than 4k), often by a factor of 10x-15x. ReiserFS also scales 
extremely well and has metadata journaling. As of kernel 2.4.18+, ReiserFS is 
solid and usable as both general-purpose filesystem and for extreme cases such 
as the creation of large filesystems, the use of many small files, very large 
files and directories containing tens of thousands of files. 
</p>

<p>
<b>XFS</b> is a filesystem with metadata journaling which comes with a robust
feature-set and is optimized for scalability. We only recommend using this
filesystem on Linux systems with high-end SCSI and/or fibre channel storage and
an uninterruptible power supply. Because XFS aggressively caches in-transit data
in RAM, improperly designed programs (those that don't take proper precautions
when writing files to disk and there are quite a few of them) can lose a good
deal of data if the system goes down unexpectedly.
</p>

<p>
<b>JFS</b> is IBM's high-performance journaling filesystem. It has recently 
become production-ready and there hasn't been a sufficient track record to 
comment positively nor negatively on its general stability at this point.
</p>

</body>
</subsection>
<subsection id="filesystems-apply">
<title>Applying a Filesystem to a Partition</title>
<body>

<p>
To create a filesystem on a partition or volume, there are tools available for 
each possible filesystem:
</p>

<table>
<tr>
  <th>Filesystem</th>
  <th>Creation Command</th>
</tr>
<tr>
  <ti>ext2</ti>
  <ti><c>mke2fs</c></ti>
</tr>
<tr>
  <ti>ext3</ti>
  <ti><c>mke2fs -j</c></ti>
</tr>
<tr>
  <ti>reiserfs</ti>
  <ti><c>mkreiserfs</c></ti>
</tr>
<tr>
  <ti>xfs</ti>
  <ti><c>mkfs.xfs</c></ti>
</tr>
<tr>
  <ti>jfs</ti>
  <ti><c>mkfs.jfs</c></ti>
</tr>
</table>

<p>
For instance, to have the root partition (<path>/dev/sda2</path> in our example)
in ext3, you would use:
</p>

<pre caption="Applying a filesystem on a partition">
# <i>mke2fs -j /dev/sda2</i>
</pre>

<p>
Now create the filesystems on your newly created partitions (or logical
volumes).
</p>

</body>
</subsection>
<subsection>
<title>Activating the Swap Partition</title>
<body>

<p>
<c>mkswap</c> is the command that is used to initialize swap partitions:
</p>

<pre caption="Creating a Swap signature">
# <i>mkswap /dev/sda1</i>
</pre>

<p>
To activate the swap partition, use <c>swapon</c>:
</p>

<pre caption="Activating the swap partition">
# <i>swapon /dev/sda1</i>
</pre>

<p>
Create and activate the swap now.
</p>

</body>
</subsection>
</section>
<section>
<title>Mounting</title>
<body>

<p>
Now that your partitions are initialized and are housing a filesystem, it is
time to mount those partitions. Use the <c>mount</c> command. Don't forget to
create the necessary mount directories for every partition you created. As an
example we mount the root and boot partition:
</p>

<pre caption="Mounting partitions">
# <i>mount /dev/sda2 /mnt/gentoo</i>
</pre>

<note>
If you want your <path>/tmp</path> to reside on a separate partition, be sure to
change its permissions after mounting: <c>chmod 1777 /mnt/gentoo/tmp</c>. This
also holds for <path>/var/tmp</path>.
</note>

<p>
We will also have to mount the proc filesystem (a virtual interface with the 
kernel) on <path>/proc</path>. But first we will need to place our files on the partitions.
</p>

<p>
Continue with <uri link="?part=1&amp;chap=5">Installing the Gentoo
Installation Files</uri>.
</p>

</body>
</section>
</sections>