ハンドブック:PPC/ブロック/ディスク

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This page is a translated version of the page Handbook:PPC/Blocks/Disks and the translation is 17% complete.


パーティション

Although it is theoretically possible to use a full disk to house a 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 partitions.

Note
In the remainder of the installation instructions, we will use the Pegasos example partition layout. Adjust to personal preference.

Designing a partition scheme

How many partitions and how big?

The number of partitions is highly dependent on the environment. For instance, if there are lots of users, then it is advised to have /home/ separate as it increases security and makes backups easier. If Gentoo is being installed to perform as a mail server, then /var/ should be separate as all mails are stored inside /var/. A good choice of filesystem will then maximize the performance. Game servers will have a separate /opt/ as most gaming servers are installed there. The reason is similar for the /home/ directory: security and backups. In most situations, /usr/ is to be kept big: not only will it contain the majority of applications, it typically also hosts the Gentoo ebuild repository (by default located at /var/db/repos/gentoo) which already takes around 650 MiB. This disk space estimate excludes the binpkgs/ and distfiles/ directories that are stored under /var/cache/ by default.

It very much depends on what the administrator wants to achieve. Separate partitions or volumes have the following advantages:

  • Choose the best performing filesystem for each partition or volume.
  • The entire system cannot run out of free space if one defunct tool is continuously writing files to a partition or volume.
  • 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).
  • Security can be enhanced by mounting some partitions or volumes read-only, nosuid (setuid bits are ignored), noexec (executable bits are ignored), etc.

However, multiple partitions have disadvantages as well. If not configured properly, the system might have lots of free space on one partition and none on another. Another nuisance is that separate partitions - especially for important mount points like /usr/ or /var/ - often require the administrator to boot with an initramfs to mount the partition before other boot scripts start. This isn't always the case though, so results may vary.

There is also a 15-partition limit for SCSI and SATA unless the disk uses GPT labels.

What about swap space?

There is no perfect value for the swap partition. The purpose of swap space is to provide disk storage to the kernel when internal memory (RAM) is under pressure. A swap space allows for the kernel to move memory pages that are not likely to be accessed soon to disk (swap or page-out), freeing memory. Of course, if that memory is suddenly needed, these pages need to be put back in memory (page-in) which will take a while (as disks are very slow compared to internal memory).

When the system is not going to run memory intensive applications or the system has lots of memory available, then it probably does not need much swap space. However, swap space is also used to store the entire memory in case of hibernation. If the system is going to need hibernation, then a bigger swap space is necessary, often at least the amount of memory installed in the system.


Apple New World

Apple New World machines are fairly straightforward to configure. The first partition is always an Apple Partition Map (APM). This partition keeps track of the layout of the disk. It is not possible to remove this partition. The next partition should always be a bootstrap partition. This partition contains a small (800KiB) HFS filesystem that holds a copy of the bootloader Yaboot and its configuration file. This partition is not the same as a /boot partition as found on other architectures. After the boot partition, the usual Linux filesystems are placed, according to the scheme below. The swap partition is a temporary storage place for when the system runs out of physical memory. The root partition will contain the filesystem that Gentoo is installed on. To dual boot, the OSX partition can go anywhere after the bootstrap partition to insure that yaboot starts first.

Note
There may be "Disk Driver" partitions on the disk such as Apple_Driver63, Apple_Driver_ATA, Apple_FWDriver, Apple_Driver_IOKit, and Apple_Patches. These are used to boot MacOS, so if there is no need for this, they can be removed by initializing the disk with mac-fdisk's i option. Be careful, this will completely erase the disk! If in doubt do not remove them.
Note
If the disk is partitioned with Apple's Disk Utility, there may be 128 MiB spaces between partitions which Apple reserves for "future use". These can be safely removed.
Partition Size Filesystem Description
/dev/sda1 32KiB None. Apple Partition Map (APM).
/dev/sda2 800KiB HFS Apple bootstrap.
/dev/sda3 512 MiB swap Linux swap (type 0x82).
/dev/sda4 Rest of the disk. ext4, reiserfs, xfs, etc. Linux root.

Apple Old World

Apple Old World machines are a bit more complicated to configure. The first partition is always an Apple Partition Map (APM). This partition keeps track of the layout of the disk. It is not possible to remove this partition. When using BootX, the configuration below assumes that MacOS is installed on a separate disk. If this is not the case, there will be additional partitions for "Apple Disk Drivers" such as Apple_Driver63, Apple_Driver_ATA, Apple_FWDriver, Apple_Driver_IOKit, Apple_Patches and the MacOS install. When using Quik, it is necessary to create a boot partition to hold the kernel, unlike other Apple boot methods. After the boot partition, the usual Linux filesystems are placed, according to the scheme below. The swap partition is a temporary storage place for when the system runs out of physical memory. The root partition will contain the filesystem that Gentoo is installed on.

Note
When using an OldWorld machine, it is necessary to keep MacOS available. The layout here assumes MacOS is installed on a separate drive.

Example partition layout for an Old World machine:

Partition Size Filesystem Description
/dev/sda1 32KiB None. Apple Partition Map (APM).
/dev/sda2 32MiB ext2 Quik Boot Partition (quik only).
/dev/sda3 512MiB swap Linux swap (type 0x82).
/dev/sda4 Rest of the disk. ext4, reiserfs, xfs, etc. Linux root.

Pegasos

The Pegasos partition layout is quite simple compared to the Apple layouts. The first partition is a boot partition, which contains kernels to be booted along with an Open Firmware script that presents a menu on boot. After the boot partition, the usual Linux filesystems are placed, according to the scheme below. The swap partition is a temporary storage place for when the system runs out of physical memory. The root partition will contain the filesystem that Gentoo is installed on.

Example partition layout for Pegasos systems:

Partition Size Filesystem Description
/dev/sda1 32MiB affs1 or ext2 Boot partition.
/dev/sda2 512MiB swap Linux swap (type 0x82).
/dev/sda3 Rest of the disk. ext4, reiserfs, xfs, etc. Linux root.

IBM PReP (RS/6000)

The IBM PowerPC Reference Platform (PReP) requires a small PReP boot partition on the disk's first partition, followed by the swap and root partitions.

Example partition layout for the IBM PReP:

Partition Size Filesystem Description
/dev/sda1 800KiB None PReP boot partition (type 0x41).
/dev/sda2 512MiB swap Linux swap (type 0x82).
/dev/sda3 Rest of the disk ext4, reiserfs, xfs, etc. Linux root (type 0x83).
Warning
parted is able to resize partitions including HFS+. Unfortunately there may be issues with resizing HFS+ journaled filesystems, so, for the best results, switch off journaling in Mac OS X before resizing. Remember that any resizing operation is dangerous, so attempt at own risk! Be sure to always have a backup of all data before resizing!

Using mac-fdisk (Apple)

At this point, create the partitions using mac-fdisk:

root #mac-fdisk /dev/sda

If Apple's Disk Utility was used prior to leave space for Linux, first delete the partitions that might have been created previously to make room for the new install. Use d in mac-fdisk to delete those partition(s). It will ask for the partition number to delete. Usually the first partition on NewWorld machines (Apple_partition_map) cannot be deleted. To start with a clean disk, simply initialize the disk by pressing i. This will completely erase the disk, so use this with caution.

Second, create an Apple_Bootstrap partition by using b. It will ask for what block to start. Enter the number of the first free partition, followed by a p. For instance this is 2p.

Note
This partition is not a /boot partition. It is not used by Linux at all; there is no need to place any filesystem on it and it should never be mounted. Apple users don't need an extra partition for /boot.

Now create a swap partition by pressing c. Again mac-fdisk will ask for what block to start this partition from. As we used 2 before to create the Apple_Bootstrap partition, now enter 3p. When sked for the size, enter 512M (or whatever size needed - a minimum of 512MiB is recommended, but 2 times the physical memory is the generally accepted size). When asked for a name, enter swap.

To create the root partition, enter c, followed by 4p to select from what block the root partition should start. When asked for the size, enter 4p again. mac-fdisk will interpret this as "Use all available space". When asked for the name, enter root.

To finish up, write the partition to the disk using w and q to quit mac-fdisk.

Note
To make sure everything is okay, run mac-fdisk -l and check whether all the partitions are there. If not all partitions created previously are shown, or the changes made are not reflected in the output, reinitialize the partitions by pressing i in mac-fdisk. Note that this will recreate the partition map and thus remove all existing partitions.

Using parted (Pegasos and RS/6000)

parted, the partition editor, can now handle HFS+ partitions used by Mac OS and Mac OS X. With this tool it is possible to resize the Mac partitions and create space for the Linux partitions. Nevertheless, the example below describes partitioning for Pegasos machines only.

To begin let's fire up parted:

root #parted /dev/sda

If the drive is unpartitioned, run mklabel amiga to create a new disklabel for the drive.

It is possible to type print at any time in parted to display the current partition table. To abort parted, press Ctrl+c.

If next to Linux, the system is also meant to have MorphOS installed, then create an affs1 filesystem at the start of the drive. 32MB should be more than enough to store the MorphOS kernel. With a Pegasos I, or when Linux will use any filesystem besides ext2 or ext3, then it is necessary to also store the Linux kernel on this partition (the Pegasos II can only boot from ext2/ext3 or affs1 partitions). To create the partition run mkpart primary affs1 START END where START and END should be replaced with the megabyte range (e.g. 0 32) which creates a 32 MB partition starting at 0MB and ending at 32MB. When creating an ext2 or ext3 partition instead, substitute ext2 or ext3 for affs1 in the mkpart command.

Create two partitions for Linux, one root filesystem and one swap partition. Run mkpart primary START END to create each partition, replacing START and END with the desired megabyte boundaries.

It is generally recommended to create a swap partition that is two times bigger than the amount of RAM in the computer, but at least 512MiB is recommended. To create the swap partition, run mkpart primary linux-swap START END with START and END again denoting the partition boundaries.

When done in parted simply type quit.