手册：MIPS/安装/准备磁盘

This page is a translated version of the page Handbook:MIPS/Installation/Disks and the translation is 100% complete.

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块设备简介

块设备

让我们来好好看看Gentoo Linux以及普通Linux中有关磁盘方面的知识，包括Linux文件系统，分区和块设备。一旦磁盘和文件的来龙去脉都了解了，我们将设置分区和文件系统的安装Gentoo Linux。

首先，让我们来看看块设备。最著名的块设备可能是代表Linux系统第一块磁盘的/dev/sda。SCSI和SATA磁盘全标为/dev/sd*；甚至IDE磁盘在libata内核框架下也标为/dev/sd*。当使用老设备框架时，第一个IDE磁盘是/dev/hda。

上面的块设备代表的抽象接口的磁盘。用户程序可以使用这些块设备来与你的磁盘进行交互，而无需担心驱动器到底是IDE，SCSI还是其他什么东西。该程序可以把磁盘当作一系列连续的，可随机访问的512字节块的存储。

Partitions

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. These are called partitions.

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 /usr/portage) which already takes around 650 MiB. This disk space estimate excludes the packages/ and distfiles/ directories that are generally stored within this ebuild repository.

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.

Using fdisk

SGI machines: Creating an SGI disk label

All disks in an SGI System require an SGI Disk Label, which serves a similar function as Sun & MS-DOS disklabels -- It stores information about the disk partitions. Creating a new SGI Disk Label will create two special partitions on the disk:

SGI Volume Header (9th partition): This partition is important. It is where the bootloader will reside, and in some cases, it will also contain the kernel images.
SGI Volume (11th partition): This partition is similar in purpose to the Sun Disklabel's third partition of "Whole Disk". This partition spans the entire disk, and should be left untouched. It serves no special purpose other than to assist the PROM in some undocumented fashion (or it is used by IRIX in some way).

Warning
The SGI Volume Header must begin at cylinder 0. Failure to do so means a failure to boot from the disk.

The following is an example excerpt from an fdisk session. Read and tailor it to personal preference...

root #fdisk /dev/sda

Switch to expert mode:

Command (m for help):x

With m the full menu of options is displayed:

Expert command (m for help):m

Command action
   b   move beginning of data in a partition
   c   change number of cylinders
   d   print the raw data in the partition table
   e   list extended partitions
   f   fix partition order
   g   create an IRIX (SGI) partition table
   h   change number of heads
   m   print this menu
   p   print the partition table
   q   quit without saving changes
   r   return to main menu
   s   change number of sectors/track
   v   verify the partition table
   w   write table to disk and exit

Build an SGI disk label:

Expert command (m for help):g

Building a new SGI disklabel. Changes will remain in memory only,
until you decide to write them. After that, of course, the previous
content will be irrecoverably lost.

Return to the main menu:

Expert command (m for help):r

Take a look at the current partition layout:

Command (m for help):p

Disk /dev/sda (SGI disk label): 64 heads, 32 sectors, 17482 cylinders
Units = cylinders of 2048 * 512 bytes
  
----- partitions -----
Pt#     Device  Info     Start       End   Sectors  Id  System
 9:  /dev/sda1               0         4     10240   0  SGI volhdr
11:  /dev/sda2               0     17481  35803136   6  SGI volume
----- Bootinfo -----
Bootfile: /unix
----- Directory Entries -----

Note
If the disk already has an existing SGI Disklabel, then fdisk will not allow the creation of a new label. There are two ways around this. One is to create a Sun or MS-DOS disklabel, write the changes to disk, and restart fdisk. The second is to overwrite the partition table with null data via the following command: dd if=/dev/zero of=/dev/sda bs=512 count=1

Resizing the SGI volume header

Important
This step is often needed, due to a bug in fdisk. For some reason, the volume header isn't created correctly, the end result being it starts and ends on cylinder 0. This prevents multiple partitions from being created. To get around this issue... read on.

Now that an SGI Disklabel is created, partitions may now be defined. In the above example, there are already two partitions defined. These are the special partitions mentioned above and should not normally be altered. However, for installing Gentoo, we'll need to load a bootloader, and possibly multiple kernel images (depending on system type) directly into the volume header. The volume header itself can hold up to eight images of any size, with each image allowed eight-character names.

The process of making the volume header larger isn't exactly straight-forward; there's a bit of a trick to it. One cannot simply delete and re-add the volume header due to odd fdisk behavior. In the example provided below, we'll create a 50MB Volume header in conjunction with a 50MB /boot/ partition. The actual layout of a disk may vary, but this is for illustrative purposes only.

Create a new partition:

Command (m for help):n

Partition number (1-16): 1
First cylinder (5-8682, default 5): 51
 Last cylinder (51-8682, default 8682): 101

Notice how fdisk only allows Partition #1 to be re-created starting at a minimum of cylinder 5? If we attempted to delete & re-create the SGI Volume Header this way, this is the same issue we would have encountered. In our example, we want /boot/ to be 50MB, so we start it at cylinder 51 (the Volume Header needs to start at cylinder 0, remember?), and set its ending cylinder to 101, which will roughly be 50MB (+/- 1-5MB).

Delete the partition:

Command (m for help):d

Partition number (1-16): 9

Now recreate it:

Command (m for help):n

Partition number (1-16): 9
First cylinder (0-50, default 0): 0
 Last cylinder (0-50, default 50): 50

If unsure how to use fdisk have a look down further at the instructions for partitioning on Cobalts. The concepts are exactly the same -- just remember to leave the volume header and whole disk partitions alone.

Once this is done, create the rest of your partitions as needed. After all the partitions are laid out, make sure to set the partition ID of the swap partition to 82, which is Linux Swap. By default, it will be 83, Linux Native.

Partitioning Cobalt drives

On Cobalt machines, the BOOTROM expects to see a MS-DOS MBR, so partitioning the drive is relatively straightforward -- in fact, it's done the same way as done for an Intel x86 machine. However there are some things you need to bear in mind.

Cobalt firmware will expect /dev/sda1 to be a Linux partition formatted EXT2 Revision 0. EXT2 Revision 1 partitions will NOT WORK! (The Cobalt BOOTROM only understands EXT2r0)
The above said partition must contain a gzipped ELF image, vmlinux.gz in the root of that partition, which it loads as the kernel

For that reason, it is recommended to create a ~20MB /boot/ partition formatted EXT2r0 upon which to install CoLo & kernels. This allows the user to run a modern filesystem (EXT3 or ReiserFS) for the root filesystem.

In the example, it is assumed that /dev/sda1 is created to mount later as a /boot/ partition. To make this /, keep the PROM's expectations in mind.

So, continuing on... To create the partitions type fdisk /dev/sda at the prompt. The main commands to know are these:

CODE List of important fdisk commands

    o: Wipe out old partition table, starting with an empty MS-DOS partition table
    n: New Partition
    t: Change Partition Type
        Use type 82 for Linux Swap, 83 for Linux FS
    d: Delete a partition
    p: Display (print) Partition Table
    q: Quit -- leaving old partition table as is.
    w: Quit -- writing partition table in the process.

root #fdisk /dev/sda

The number of cylinders for this disk is set to 19870.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
   (e.g., DOS FDISK, OS/2 FDISK)

Start by clearing out any existing partitions:

Command (m for help):o

Building a new DOS disklabel. Changes will remain in memory only,
until you decide to write them. After that, of course, the previous
content won't be recoverable.
  
  
The number of cylinders for this disk is set to 19870.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
   (e.g., DOS FDISK, OS/2 FDISK)
Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

Now verify the partition table is empty using the p command:

Command (m for help):p

Disk /dev/sda: 10.2 GB, 10254827520 bytes
16 heads, 63 sectors/track, 19870 cylinders
Units = cylinders of 1008 * 512 = 516096 bytes
  
   Device Boot      Start         End      Blocks   Id  System

Create the /boot partition:

Command (m for help):n

Command action
   e   extended
   p   primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-19870, default 1):
Last cylinder or +size or +sizeM or +sizeK (1-19870, default 19870): +20M

When printing the partitions, notice the newly created one:

Command (m for help):p

Disk /dev/sda: 10.2 GB, 10254827520 bytes
16 heads, 63 sectors/track, 19870 cylinders
Units = cylinders of 1008 * 512 = 516096 bytes
  
   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1          40       20128+  83  Linux

Let's now create an extended partition that covers the remainder of the disk. In that extended partition, we'll create the rest (logical partitions):

Command (m for help):n

Command action
   e   extended
   p   primary partition (1-4)
e
Partition number (1-4): 2
First cylinder (41-19870, default 41):
Using default value 41
Last cylinder or +size or +sizeM or +sizeK (41-19870, default 19870):
Using default value 19870

Now we create the / partition, /usr, /var, et.

Command (m for help):n

Command action
   l   logical (5 or over)
   p   primary partition (1-4)
l
First cylinder (41-19870, default 41):<Press ENTER>
Using default value 41
Last cylinder or +size or +sizeM or +sizeK (41-19870, default 19870): +500M

Repeat this as needed.

Last but not least, the swap space. It is recommended to have at least 250MB swap, preferrably 1GB:

Command (m for help):n

Command action
   l   logical (5 or over)
   p   primary partition (1-4)
l
First cylinder (17294-19870, default 17294): <Press ENTER>
Using default value 17294
Last cylinder or +size or +sizeM or +sizeK (1011-19870, default 19870): <Press ENTER>
Using default value 19870

When checking the partition table, everything should be ready - one thing notwithstanding.

Command (m for help):p

Disk /dev/sda: 10.2 GB, 10254827520 bytes
16 heads, 63 sectors/track, 19870 cylinders
Units = cylinders of 1008 * 512 = 516096 bytes
  
Device Boot      Start         End      Blocks      ID  System
/dev/sda1               1          21       10552+  83  Linux
/dev/sda2              22       19870    10003896    5  Extended
/dev/sda5              22        1037      512032+  83  Linux
/dev/sda6            1038        5101     2048224+  83  Linux
/dev/sda7            5102        9165     2048224+  83  Linux
/dev/sda8            9166       13229     2048224+  83  Linux
/dev/sda9           13230       17293     2048224+  83  Linux
/dev/sda10          17294       19870     1298776+  83  Linux

Notice how #10, the swap partition is still type 83? Let's change that to the proper type:

Command (m for help):t

Partition number (1-10): 10
Hex code (type L to list codes): 82
Changed system type of partition 10 to 82 (Linux swap)

Now verify:

Command (m for help):p

Disk /dev/sda: 10.2 GB, 10254827520 bytes
16 heads, 63 sectors/track, 19870 cylinders
Units = cylinders of 1008 * 512 = 516096 bytes
  
Device Boot      Start         End      Blocks      ID  System
/dev/sda1               1          21       10552+  83  Linux
/dev/sda2              22       19870    10003896    5  Extended
/dev/sda5              22        1037      512032+  83  Linux
/dev/sda6            1038        5101     2048224+  83  Linux
/dev/sda7            5102        9165     2048224+  83  Linux
/dev/sda8            9166       13229     2048224+  83  Linux
/dev/sda9           13230       17293     2048224+  83  Linux
/dev/sda10          17294       19870     1298776+  82  Linux Swap

We write out the new partition table:

Command (m for help):w

The partition table has been altered!
  
Calling ioctl() to re-read partition table.
Syncing disks.

创建文件系统

介绍

现在分区已经创建，该在上面设置文件系统了。下一章节中描述了Linux所支持的众多文件系统。知道使用哪一个文件系统的读者可以继续阅读为分区应用文件系统。剩下的人应该学习可用的文件系统……

文件系统

有一些可以使用的文件系统。有些在mips架构上稳定——建议在选择为一个重要分区实验性的选择文件系统前继续阅读。

btrfs: 是下一代文件系统，提供了许多高级功能，如快照，通过校验和自我修复、透明压缩、子卷和集成 RAID。几个发行版已经开始将它作为一个默认的选项,但它还未为生产工作做好准备。文件系统报告崩溃是常见的。其开发人员敦促人们运行最新的内核版本来解决安全问题,以及老的问题。这种情况已经很多年了,现在使用它还为时过早。如果出现变更，以及发生了变化，解决错误问题，都很少往旧内核注入补丁。请谨慎使用这个文件系统!
ext2: 是经考验证明可靠的Linux文件系统，但是没有元数据日志，这意味这在启动系统时的ext2文件系统的日常检查相当耗时。现在相当一部分的新一代的日志文件系统都可以非常迅速检查一致性，因此比那些非日志文件系统更受欢迎。当你启动系统碰巧遇到文件系统状态不一致时，日志文件系统不会在那里耽搁很长时间。
ext3: 是ext2文件系统的带日志版本，提供了元数据日志模式以快速恢复数据。此外还提供了其他增强的日志模式，如完整数据日志模式和有序数据日志模式。它使用了HTree索引，在几乎所有的情况下都能保持高性能。简而言之，ext3是非常好及可靠的文件系统。
ext4: 最初创建为ext3的一个分支，EXT4带来了新的功能，性能改进和去除中度更改磁盘格式大小限制。它可以跨越体积高达1的EB并用16 TB最大文件大小。取而代之的是经典的ext2/3位块分配的ext4的使用范围，这对提高大文件的性能，并减少碎片。的Ext4还提供了更为复杂的块分配算法（延迟分配和多嵌段分配）给文件系统驱动更多的方式来优化数据的布局在磁盘上。 EXT4是推荐的通用所有平台的文件系统。
f2fs: 这个文件系统最初由三星创建用于NAND闪存，是一种闪存文件系统从直到2016年第二季度起，这个文件系统仍然被认为不成熟。把Gentoo安装到microSD卡，USB驱动器或其他基于闪存的存储设备时使用它是一个不错的选择。
JFS: 是IBM的高性能日志文件系统。JFS是一个轻量级的、快速的和稳定的基于B+树的文件系统，在很多情况下都有很好的表现。
ReiserFS: 是基于B+树的文件系统，它有着非常全面的性能，特别时在处理很多小文件的时候，虽然会占用多一点CPU。ReiserFS相比其他文件系统显得受维护的不够。
XFS: 是一种带元数据日志的文件系统，它有一个健壮的特性集，并且对可伸缩性进行了优化。XFS似乎对各种各样的硬件问题显得不够宽容。
vfat: 也称为FAT32，被支持Linux，但不支持任何权限设置。它主要用于互操作性与其他操作系统（主要是微软的Windows），但也是很有必要的一些系统固件（如UEFI）的支持。
NTFS: 这个“新技术”的文件系统是Microsoft Windows的旗舰文件系统。与上面的vfat类似，它不存储BSD或Linux正常工作所需的权限设置或扩展属性，因此它不能用作根文件系统。它应该'只'用于与Microsoft Windows系统的互操作性（注意只强调）。

当在一个小的分区（少于8GB）上使用ext2、ext3或ext4，则创建文件系统时必须带适当的选项以保留足够的inode。mke2fs（mkfs.ext2）应用程序使用“字节每inode”设置来计算一个文件系统应该用多少个inode。在小分区，建议增加计算出的inode数量。

对于ext2，可以使用下面的命令来完成：

root #mkfs.ext2 -T small /dev/<device>

对于ext3或ext4，添加-j选项来启用日志：

root #mkfs.ext2 -j -T small /dev/<device>

这一般将是对于给定的文件系统inode数量的四倍，它的“字节每inode”从16kB每个减少到4kB每个。这个可以在将来通过提供比例进行调整：

root #mkfs.ext2 -i <ratio> /dev/<device>

为分区应用文件系统

在一个分区或卷上创建一个文件系统，这里有用于每一个可能的分区的工具。单击下表中的文件系统名称，了解每个文件系统的更多信息：

文件系统	创建命令	在最小化CD？	包
btrfs	mkfs.btrfs	Yes	sys-fs/btrfs-progs
ext2	mkfs.ext2	Yes	sys-fs/e2fsprogs
ext3	mkfs.ext3	Yes	sys-fs/e2fsprogs
ext4	mkfs.ext4	Yes	sys-fs/e2fsprogs
f2fs	mkfs.f2fs	Yes	sys-fs/f2fs-tools
jfs	mkfs.jfs	Yes	sys-fs/jfsutils
reiserfs	mkfs.reiserfs	Yes	sys-fs/reiserfsprogs
xfs	mkfs.xfs	Yes	sys-fs/xfsprogs
vfat	mkfs.vfat	Yes	sys-fs/dosfstools
NTFS	mkfs.ntfs	Yes	sys-fs/ntfs3g

比如，在示例分区结构中，有使用ext2的引导分区（/dev/sda1）和使用ext4的根分区（/dev/sda5），下面的命令将会用到：

root #mkfs.ext2 /dev/sda1

root #mkfs.ext4 /dev/sda5

现在在新创建的分区（或逻辑卷）上创建文件系统。

激活swap分区

mkswap是用来初始化swap分区的命令：

root #mkswap /dev/sda10

要激活swap分区，使用swapon：

root #swapon /dev/sda10

使用上面提到的命令创建和激活swap。

挂载 root 分区

现在分区都已初始化并有文件系统，接下来该挂载那些分区了。使用mount命令，但是不要忘记为每一个创建的分区创建需要的挂载目录。比如示例中我们挂载根分区:

root #mount /dev/sda5 /mnt/gentoo

附注
如果/tmp/需要放在一个独立分区，确保在挂载后变更它的权限：

root #chmod 1777 /mnt/gentoo/tmp

这同样适用于/var/tmp。

后面的介绍中将挂载proc文件系统（一个内核的虚拟接口）和其它内核伪文件系统。不过我们首先安装Gentoo安装文件。

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