en/handbook/hb-install-ppc64-disk.xml

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<sections>
<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 IDE drive in a Linux system, namely
<path>/dev/hda</path>. If your system uses SCSI drives, then your first hard
drive would be <path>/dev/sda</path>. Serial ATA drives are also
<path>/dev/sda</path> even if they are IDE drives.
</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>Partitions and 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 most systems,
these are called <e>partitions</e>. Other architectures use a similar technique,
called <e>slices</e>.
</p>

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

<p>
If you are not interested in drawing up a partitioning scheme for your system,
you can use the partitioning scheme we use throughout this book:
</p>

<table>
<tr>
  <th>Partition</th>
  <th>Filesystem</th>
  <th>Size</th>
  <th>Description</th>
</tr>
<tr>
  <ti><path>/dev/sda1</path></ti>
  <ti>Partition map</ti>
  <ti>31.5k</ti>
  <ti>Partition map</ti>
</tr>
<tr>
  <ti><path>/dev/sda2</path></ti>
  <ti>(bootstrap)</ti>
  <ti>800k</ti>
  <ti>Apple_Bootstrap</ti>
</tr>
<tr>
  <ti><path>/dev/sda3</path></ti>
  <ti>(swap)</ti>
  <ti>512M</ti>
  <ti>Swap partition</ti>
</tr>
<tr>
  <ti><path>/dev/sda4</path></ti>
  <ti>ext3</ti>
  <ti>Rest of the disk</ti>
  <ti>Root partition</ti>
</tr>
</table>

<note>
There are some partitions named like this: <path>Apple_Driver43,
Apple_Driver_ATA, Apple_FWDriver, Apple_Driver_IOKit,
Apple_Patches</path>. If you are not planning to use MacOS 9 you can
delete them, because MacOS X and Linux don't need them.
You might have to use parted in order to delete them, as mac-fdisk can't delete them yet.
</note>

<p>
If you are interested in knowing how big a partition should be, or even how 
many partitions you need, read on. Otherwise continue now with
<uri link="#mac-fdisk">Apple G5: Using mac-fdisk to Partition your
Disk</uri> or <uri link="#fdisk">IBM pSeries: 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. There is also a 15-partition
limit for SCSI and SATA.
</p>

</body>
</subsection>
</section>
<section id="mac-fdisk">
<title>Default: Using mac-fdisk (Apple G5) Partition your Disk</title>
<body>

<p>
At this point, create your partitions using <c>mac-fdisk</c>:
</p>

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

<p>
First delete the partitions you have cleared previously to make room for your
Linux partitions. Use <c>d</c> in <c>mac-fdisk</c> to delete those partition(s).
It will ask for the partition number to delete.
</p>

<p>
Second, create an <e>Apple_Bootstrap</e> partition by using <c>b</c>. It will
ask for what block you want to start. Enter the number of your first free
partition, followed by a <c>p</c>. For instance this is <c>1p</c>.
</p>

<note>
This partition is <e>not</e> a "boot" partition. It is not used by Linux at all;
you don't have to place any filesystem on it and you should never mount it. PPC
users don't need a an extra partition for <path>/boot</path>.
</note>

<p>
Now create a swap partition by pressing <c>c</c>. Again <c>mac-fdisk</c> will
ask for what block you want to start this partition from. As we used <c>1</c>
before to create the Apple_Bootstrap partition, you now have to enter
<c>2p</c>. When you're asked for the size, enter <c>512M</c> (or whatever size
you want -- 512MB is recommended though). When asked for a name, enter <c>swap</c>
(mandatory).
</p>

<p>
To create the root partition, enter <c>c</c>, followed by <c>3p</c> to select
from what block the root partition should start. When asked for the size, enter
<c>3p</c> again. <c>mac-fdisk</c> will interpret this as "Use all available
space". When asked for the name, enter <c>root</c> (mandatory).
</p>

<p>
To finish up, write the partition to the disk using <c>w</c> and <c>q</c> to
quit <c>mac-fdisk</c>.
</p>
    
<note>
To make sure everything is ok, you should run mac-fdisk once more and check whether all the partitions are there. 
If you don't see any of the partitions you created, or the changes you made, you should reinitialize your partitions by pressing "i" in mac-fdisk. 
Note that this will recreate the partition map and thus remove all your partitions. 
</note>
    
<p>
Now that your partitions are created, you can now continue with <uri
link="#filesystems">Creating Filesystems</uri>.
</p>

</body>
</section>
<section id="fdisk">
<title>IBM pSeries: using fdisk to Partition your Disk</title>
<subsection>
<body>

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

<table>
<tr>
  <th>Partition</th>
  <th>Description</th>
</tr>
<tr>
  <ti><path>/dev/sda1</path></ti>
  <ti>PPC PReP 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>Viewing the Current Partition Layout</title>
<body>

<p>
<c>fdisk</c> is a popular and powerful tool to split your disk into
partitions.  Fire up <c>fdisk</c> on your disk (in our example, we
use <path>/dev/sda</path>):
</p>

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

<p>
Once in <c>fdisk</c>, you'll be greeted with a prompt that looks like
this:
</p>

<pre caption="fdisk prompt">
Command (m for help):
</pre>

<p>
Type <c>p</c> to display your disk's current partition configuration:
</p>

<pre caption="An example partition configuration">
Command (m for help): p

Disk /dev/sda: 30.7 GB, 30750031872 bytes
141 heads, 63 sectors/track, 6761 cylinders
Units = cylinders of 8883 * 512 = 4548096 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/hdb1               1          12       53266+  83  Linux
/dev/hdb2              13         233      981571+  82  Linux swap
/dev/hdb3             234         674     1958701+  83  Linux
/dev/hdb4             675        6761    27035410+   5  Extended
/dev/hdb5             675        2874     9771268+  83  Linux
/dev/hdb6            2875        2919      199836   83  Linux
/dev/hdb7            2920        3008      395262   83  Linux
/dev/hdb8            3009        6761    16668918   83  Linux

Command (m for help):
</pre>

<p>
This particular disk is configured to house seven Linux filesystems
(each with a corresponding partition listed as "Linux") as well as a
swap partition (listed as "Linux swap").
</p>

</body>
</subsection>
<subsection>
<title>Removing all Partitions</title>
<body>

<p>
We will first remove all existing partitions from the disk. Type
<c>d</c> to delete a partition. For instance, to delete an existing
<path>/dev/sda1</path>:
</p>

<note>If you don't want to delete all partitions just delete those you
want to delete. At this point the author recommends a backup of your
data to avoid the lose of it.
</note>

<pre caption="Deleting a partition">
Command (m for help): <i>d</i>
Partition number (1-4): <i>1</i>
</pre>

<p>
The partition has been scheduled for deletion. It will no longer show up
if you type <c>p</c>, but it will not be erased until your changes have
been saved. If you made a mistake and want to abort without saving your
changes, type <c>q</c> immediately and hit enter and your partition will
not be deleted.
</p>

<p>
Now, assuming that you do indeed want to wipe out all the partitions on
your system, repeatedly type <c>p</c> to print out a partition listing
and then type <c>d</c> and the number of the partition to delete it.
Eventually, you'll end up with a partition table with nothing in it:
</p>

<pre caption="An empty partition table">
Disk /dev/sda: 30.7 GB, 30750031872 bytes
141 heads, 63 sectors/track, 6761 cylinders
Units = cylinders of 8883 * 512 = 4548096 bytes

Device Boot    Start       End    Blocks   Id  System

Command (m for help):
</pre>

<p>
Now that the in-memory partition table is empty, we're ready to create
the partitions. We will use a default partitioning scheme as discussed
previously. Of course, don't follow these instructions to the letter if
you don't want the same partitioning scheme!
</p>

</body>
</subsection>
<subsection>
<title>Creating the PPC PReP boot partition</title>
<body>

<p>
We first create a small PReP boot partition. Type <c>n</c> to create a new
partition, then <c>p</c> to select a primary partition, followed by
<c>1</c> to select the first primary partition. When prompted for the
first cylinder, hit enter. When prompted for the last cylinder, type
<c>+7M</c> to create a partition 7 Mbyte in size. After you've done
this, type <c>t</c> to set the partition type, <c>1</c> to select the
partition you just created and then type in <c>41</c> to set the
partition type to "PPC PReP Boot".
</p>

<note>
The PReP partition has to be smaller than 8 MByte!
</note>

<pre caption="Crating to PReP boot partition">
Command (m for help): <i>p</i>

Disk /dev/sda: 30.7 GB, 30750031872 bytes
141 heads, 63 sectors/track, 6761 cylinders
Units = cylinders of 8883 * 512 = 4548096 bytes

   Device Boot      Start         End      Blocks   Id  System

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 (1-6761, default 1): 
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-6761, default
6761): <i>+8M</i>

Command (m for help): <i>t</i>
Selected partition 1
Hex code (type L to list codes): <i>41</i>
Changed system type of partition 1 to 41 (PPC PReP Boot)

Command (m for help):
</pre>

<p>
Now, when you type <c>p</c>, you should see the following partition
printout:
</p>

<pre caption="Created boot partition">
Command (m for help): <i>p</i>

Disk /dev/sda: 30.7 GB, 30750031872 bytes
141 heads, 63 sectors/track, 6761 cylinders
Units = cylinders of 8883 * 512 = 4548096 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/hdb1               1           3       13293   41  PPC PReP Boot

Command (m for help):
</pre>
</body>
</subsection>
<subsection>
<title>Creating the Swap Partition</title>
<body>

<p>
Let's now create the swap partition. To do this, type <c>n</c> to create
a new partition, then <c>p</c> to tell fdisk that you want a primary
partition. Then type <c>2</c> to create the second primary partition,
<path>/dev/sda2</path> in our case. When prompted for the first
cylinder, hit enter. When prompted for the last cylinder, type
<c>+512M</c> to create a partition 512MB in size. After you've done
this, type <c>t</c> to set the partition type, <c>2</c> to select the
partition you just created and then type in <c>82</c> to set the
partition type to "Linux Swap". After completing these steps, typing
<c>p</c> should display a partition table that looks similar to this:
</p>

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

Disk /dev/sda: 30.7 GB, 30750031872 bytes
141 heads, 63 sectors/track, 6761 cylinders
Units = cylinders of 8883 * 512 = 4548096 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/hdb1               1           3       13293   41  PPC PReP Boot
/dev/hdb2               4         117      506331   82  Linux swap

Command (m for help):
</pre>

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

<p>
Finally, let's create the root partition. To do this, type <c>n</c> to
create a new partition, then <c>p</c> to tell fdisk that you want a
primary partition. Then type <c>3</c> to create the third primary
partition, <path>/dev/sda3</path> in our case. When prompted for the
first cylinder, hit enter. When prompted for the last cylinder, hit
enter to create a partition that takes up the rest of the remaining
space on your disk. After completing these steps, typing <c>p</c> should
display a partition table that looks similar to this:
</p>

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

Disk /dev/sda: 30.7 GB, 30750031872 bytes
141 heads, 63 sectors/track, 6761 cylinders
Units = cylinders of 8883 * 512 = 4548096 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/hdb1               1           3       13293   41  PPC PReP Boot
/dev/hdb2               4         117      506331   82  Linux swap
/dev/hdb3             118        6761    29509326   83  Linux

Command (m for help):
</pre>
</body>
</subsection>
<subsection>
<title>Saving the Partition Layout</title>
<body>

<p>
To save the partition layout and exit <c>fdisk</c>, type <c>w</c>.
</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>
<subsection>
<title>Filesystems?</title>
<body>

<note>
Several filesystems are available. Ext2 and ext3 are found stable on the
PPC64 architecture, reiserfs and xfs are in experimental stage. jfs is
unsupported.
</note>

<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 that is fully supported 
under Gentoo Linux's xfs-sources kernel. It 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 a 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/sda4</path> in our example)
in ext3 (as in our example), you would use:
</p>

<pre caption="Applying a filesystem on a partition">
# <i>mke2fs -j /dev/sda4</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/sda3</i>
</pre>

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

<pre caption="Activating the swap partition">
# <i>swapon /dev/sda3</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 create a mount-point and mount the root and boot partition:
</p>

<pre caption="Mounting partitions">
# <i>mkdir /mnt/gentoo</i>
# <i>mount /dev/sda4 /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>
Finally we have to create the <path>/dev</path> files in our new home, which is
needed during the bootloader installation.  This could be done by "bind"-mapping
the <path>/dev</path>-filesystem from the LiveCD:
</p>

<pre caption="Bind-mounting the /dev-filesystem">
# <i>mkdir /mnt/gentoo/dev</i>
# <i>mount -o bind /dev /mnt/gentoo/dev</i>
</pre>

<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>