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1 <?xml version='1.0' encoding='UTF-8'?>
2 <!DOCTYPE sections SYSTEM "/dtd/book.dtd">
4 <!-- The content of this document is licensed under the CC-BY-SA license -->
5 <!-- See http://creativecommons.org/licenses/by-sa/1.0 -->
7 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-install-mips-disk.xml,v 1.3 2004/07/18 10:29:59 neysx Exp $ -->
9 <sections>
10 <section>
11 <title>Introduction to Block Devices</title>
12 <subsection>
13 <title>Block Devices</title>
14 <body>
16 <p>
17 We'll take a good look at disk-oriented aspects of Gentoo Linux
18 and Linux in general, including Linux filesystems, partitions and block devices.
19 Then, once you're familiar with the ins and outs of disks and filesystems,
20 you'll be guided through the process of setting up partitions and filesystems
21 for your Gentoo Linux installation.
22 </p>
24 <p>
25 To begin, we'll introduce <e>block devices</e>. The most famous block device is
26 probably the one that represents the first SCSI HD in a Linux system, namely
27 <path>/dev/sda</path>.
28 </p>
30 <p>
31 The block devices above represent an abstract interface to the disk. User
32 programs can use these block devices to interact with your disk without worrying
33 about whether your drives are IDE, SCSI or something else. The program can
34 simply address the storage on the disk as a bunch of contiguous,
35 randomly-accessible 512-byte blocks.
36 </p>
38 </body>
39 </subsection>
40 <subsection>
41 <title>Partitions</title>
42 <body>
44 <p>
45 Although it is theoretically possible to use a full disk to house your Linux
46 system, this is almost never done in practice. Instead, full disk block devices
47 are split up in smaller, more manageable block devices. These are called
48 <e>partitions</e>.
49 </p>
51 </body>
52 </subsection>
53 </section>
54 <section>
55 <title>Designing a Partitioning Scheme</title>
56 <subsection>
57 <title>How Many and How Big?</title>
58 <body>
60 <p>
61 The number of partitions is highly dependent on your environment. For instance,
62 if you have lots of users, you will most likely want to have your
63 <path>/home</path> separate as it increases security and makes backups easier.
64 If you are installing Gentoo to perform as a mailserver, your
65 <path>/var</path> should be separate as all mails are stored inside
66 <path>/var</path>. A good choice of filesystem will then maximise your
67 performance. Gameservers will have a separate <path>/opt</path> as most gaming
68 servers are installed there. The reason is similar for <path>/home</path>:
69 security and backups.
70 </p>
72 <p>
73 As you can see, it very much depends on what you want to achieve. Separate
74 partitions or volumes have the following advantages:
75 </p>
77 <ul>
78 <li>
79 You can choose the best performing filesystem for each partition or volume
80 </li>
81 <li>
82 Your entire system cannot run out of free space if one defunct tool is
83 continuously writing files to a partition or volume
84 </li>
85 <li>
86 If necessary, file system checks are reduced in time, as multiple checks can
87 be done in parallel (although this advantage is more with multiple disks than
88 it is with multiple partitions)
89 </li>
90 <li>
91 Security can be enhanced by mounting some partitions or volumes read-only,
92 nosuid (setuid bits are ignored), noexec (executable bits are ignored) etc.
93 </li>
94 </ul>
96 <p>
97 However, multiple partitions have one big disadvantage: if not configured
98 properly, you might result in having a system with lots
99 of free space on one partition and none on another.
100 </p>
102 </body>
103 </subsection>
104 </section>
105 <section>
106 <title>Using fdisk on MIPS to Partition your Disk</title>
107 <subsection>
108 <title>Creating an SGI Disk Label</title>
109 <body>
111 <p>
112 All disks in an SGI System require an <e>SGI Disk Label</e>, which serves a
113 similar function as Sun &amp; MS-DOS disklabels -- It stores information about
114 the disk partitions. Creating a new SGI Disk Label will create two special
115 partitions on the disk:
116 </p>
118 <ul>
119 <li>
120 <e>SGI Volume Header</e> (9th partition): This partition is important. It
121 is where the kernel images will go. To store kernel images, you will utilize
122 the tool known as <c>dvhtool</c> to copy kernel images to this partition.
123 You will then be able to boot kernels from this partition via the SGI PROM
124 Monitor.
125 </li>
126 <li>
127 <e>SGI Volume</e> (11th partition): This partition is similar in purpose to
128 the Sun Disklabel's third partition of "Whole Disk". This partition spans
129 the entire disk, and should be left untouched. It serves no special purpose
130 other than to assist the PROM in some undocumented fashion (or it is used by
131 IRIX in some way).
132 </li>
133 </ul>
135 <warn>
136 The SGI Volume Header <e>must</e> begin at cylinder 0. Failure to do so means
137 you won't be able to boot from the disk.
138 </warn>
140 <p>
141 The following is an example excerpt from an <c>fdisk</c> session. Read and
142 tailor it to your needs...
143 </p>
145 <pre caption="Creating an SGI Disklabel">
146 # <i>fdisk /dev/sda</i>
148 Command (m for help): <i>x</i>
150 Expert command (m for help): <i>m</i>
151 Command action
152 b move beginning of data in a partition
153 c change number of cylinders
154 d print the raw data in the partition table
155 e list extended partitions
156 f fix partition order
157 g create an IRIX (SGI) partition table
158 h change number of heads
159 m print this menu
160 p print the partition table
161 q quit without saving changes
162 r return to main menu
163 s change number of sectors/track
164 v verify the partition table
165 w write table to disk and exit
167 Expert command (m for help): <i>g</i>
168 Building a new SGI disklabel. Changes will remain in memory only,
169 until you decide to write them. After that, of course, the previous
170 content will be unrecoverably lost.
172 Expert command (m for help): <i>r</i>
174 Command (m for help): <i>p</i>
176 Disk /dev/sda (SGI disk label): 64 heads, 32 sectors, 17482 cylinders
177 Units = cylinders of 2048 * 512 bytes
179 ----- partitions -----
180 Pt# Device Info Start End Sectors Id System
181 9: /dev/sda1 0 4 10240 0 SGI volhdr
182 11: /dev/sda2 0 17481 35803136 6 SGI volume
183 ----- Bootinfo -----
184 Bootfile: /unix
185 ----- Directory Entries -----
187 Command (m for help):
188 </pre>
190 <note>
191 If your disk already has an existing SGI Disklabel, then fdisk will not allow
192 the creation of a new label. There are two ways around this. One is to create a
193 Sun or MS-DOS disklabel, write the changes to disk, and restart fdisk. The
194 second is to overwrite the partition table with null data via the following
195 command: <c>dd if=/dev/zero of=/dev/sda bs=512 count=1</c>.
196 </note>
198 </body>
199 </subsection>
200 <subsection>
201 <title>Getting the SGI Volume Header to just the right size</title>
202 <body>
204 <p>
205 Now that an SGI Disklabel is created, partitions may now be defined. In the
206 above example, there are already two partitions defined for you. These are the
207 special partitions mentioned above and should not normally be altered. However,
208 for installing Gentoo, we'll need to load multiple kernel images directly into
209 the volume header, as there is no supported SGI Bootloader available in Portage
210 yet. The volume header itself can hold up to <e>eight</e> images of any size,
211 with each image allowed eight-character names.
212 </p>
214 <p>
215 The process of making the volume header larger isn't exactly straight-forward --
216 there's a bit of a trick to it. One cannot simply delete and re-add the volume
217 header due to odd fdisk behavior. In the example provided below, we'll create a
218 50MB Volume header in conjunction with a 50MB /boot partition. The actual layout
219 of your disk may vary, but this is for illustrative purposes only.
220 </p>
222 <pre caption="Resizing the SGI Volume Header correctly">
223 Command (m for help): <i>n</i>
224 Partition number (1-16): <i>1</i>
225 First cylinder (5-8682, default 5): <i>51</i>
226 Last cylinder (51-8682, default 8682): <i>101</i>
227 <comment>(Notice how fdisk only allows Partition #1 to be re-created starting at a minimum of cylinder 5)</comment>
228 <comment>(Had you attempted to delete &amp; re-create the SGI Volume Header this way, this is the same issue
229 you would have encountered.)</comment>
230 <comment>(In our example, we want /boot to be 50MB, so we start it at cylinder 51 (the Volume Header needs to
231 start at cylinder 0, remember?), and set its ending cylinder to 101, which will roughly be 50MB (+/- 1-5MB))</comment>
233 Command (m for help): <i>d</i>
234 Partition number (1-16): <i>9</i>
235 <comment>(Delete Partition #9 (SGI Volume Header))</comment>
237 Command (m for help): <i>n</i>
238 Partition number (1-16): <i>9</i>
239 First cylinder (0-50, default 0): <i>0</i>
240 Last cylinder (0-50, default 50): <i>50</i>
241 <comment>(Re-Create Partition #9, ending just before Partition #1)</comment>
242 </pre>
244 </body>
245 </subsection>
246 <subsection>
247 <title>Final partition layout</title>
248 <body>
250 <p>
251 Once this is done, you are safe to create the rest of your partitions as you see
252 fit. After all your partitions are laid out, make sure you set the partition ID
253 of your swap partition to <c>82</c>, which is Linux Swap. By default, it will be
254 <c>83</c>, Linux Native.
255 </p>
257 <p>
258 Now that your partitions are created, you can now continue with <uri
259 link="#filesystems">Creating Filesystems</uri>.
260 </p>
262 </body>
263 </subsection>
264 </section>
265 <section id="filesystems">
266 <title>Creating Filesystems</title>
267 <subsection>
268 <title>Introduction</title>
269 <body>
271 <p>
272 Now that your partitions are created, it is time to place a filesystem on them.
273 If you don't care about what filesystem to choose and are happy with what we use
274 as default in this handbook, continue with <uri
275 link="#filesystems-apply">Applying a Filesystem to a Partition</uri>.
276 Otherwise read on to learn about the available filesystems...
277 </p>
279 </body>
280 </subsection>
281 <subsection>
282 <title>Filesystems?</title>
283 <body>
285 <p>
286 Several filesystems are available. Ext2 and ext3 are found stable on the
287 MIPS architectures, others are experimental.
288 </p>
290 <p>
291 <b>ext2</b> is the tried and true Linux filesystem but doesn't have metadata
292 journaling, which means that routine ext2 filesystem checks at startup time can
293 be quite time-consuming. There is now quite a selection of newer-generation
294 journaled filesystems that can be checked for consistency very quickly and are
295 thus generally preferred over their non-journaled counterparts. Journaled
296 filesystems prevent long delays when you boot your system and your filesystem
297 happens to be in an inconsistent state.
298 </p>
300 <p>
301 <b>ext3</b> is the journaled version of the ext2 filesystem, providing metadata
302 journaling for fast recovery in addition to other enhanced journaling modes like
303 full data and ordered data journaling. ext3 is a very good and reliable
304 filesystem. It has an additional hashed b-tree indexing option that enables
305 high performance in almost all situations. In short, ext3 is an excellent
306 filesystem.
307 </p>
309 <p>
310 <b>ReiserFS</b> is a B*-tree based filesystem that has very good overall
311 performance and greatly outperforms both ext2 and ext3 when dealing with small
312 files (files less than 4k), often by a factor of 10x-15x. ReiserFS also scales
313 extremely well and has metadata journaling. As of kernel 2.4.18+, ReiserFS is
314 solid and usable as both general-purpose filesystem and for extreme cases such
315 as the creation of large filesystems, the use of many small files, very large
316 files and directories containing tens of thousands of files.
317 </p>
319 <p>
320 <b>XFS</b> is a filesystem with metadata journaling which comes with a robust
321 feature-set and is optimized for scalability. We only recommend using this
322 filesystem on Linux systems with high-end SCSI and/or fibre channel storage and
323 an uninterruptible power supply. Because XFS aggressively caches in-transit data
324 in RAM, improperly designed programs (those that don't take proper precautions
325 when writing files to disk and there are quite a few of them) can lose a good
326 deal of data if the system goes down unexpectedly.
327 </p>
329 <p>
330 <b>JFS</b> is IBM's high-performance journaling filesystem. It has recently
331 become production-ready and there hasn't been a sufficient track record to
332 comment positively nor negatively on its general stability at this point.
333 </p>
335 </body>
336 </subsection>
337 <subsection id="filesystems-apply">
338 <title>Applying a Filesystem to a Partition</title>
339 <body>
341 <p>
342 To create a filesystem on a partition or volume, there are tools available for
343 each possible filesystem:
344 </p>
346 <table>
347 <tr>
348 <th>Filesystem</th>
349 <th>Creation Command</th>
350 </tr>
351 <tr>
352 <ti>ext2</ti>
353 <ti><c>mke2fs</c></ti>
354 </tr>
355 <tr>
356 <ti>ext3</ti>
357 <ti><c>mke2fs -j</c></ti>
358 </tr>
359 <tr>
360 <ti>reiserfs</ti>
361 <ti><c>mkreiserfs</c></ti>
362 </tr>
363 <tr>
364 <ti>xfs</ti>
365 <ti><c>mkfs.xfs</c></ti>
366 </tr>
367 <tr>
368 <ti>jfs</ti>
369 <ti><c>mkfs.jfs</c></ti>
370 </tr>
371 </table>
373 <p>
374 For instance, to have the boot partition (<path>/dev/sda1</path> in our
375 example) in ext2 and the root partition (<path>/dev/sda3</path> in our example)
376 in ext3, you would use:
377 </p>
379 <pre caption="Applying a filesystem on a partition">
380 # <i>mke2fs /dev/sda1</i>
381 # <i>mke2fs -j /dev/sda3</i>
382 </pre>
384 <p>
385 Now create the filesystems on your newly created partitions (or logical
386 volumes).
387 </p>
389 </body>
390 </subsection>
391 <subsection>
392 <title>Activating the Swap Partition</title>
393 <body>
395 <p>
396 <c>mkswap</c> is the command that is used to initialize swap partitions:
397 </p>
399 <pre caption="Creating a Swap signature">
400 # <i>mkswap /dev/sda2</i>
401 </pre>
403 <p>
404 To activate the swap partition, use <c>swapon</c>:
405 </p>
407 <pre caption="Activating the swap partition">
408 # <i>swapon /dev/sda2</i>
409 </pre>
411 <p>
412 Create and activate the swap now.
413 </p>
415 </body>
416 </subsection>
417 </section>
418 <section>
419 <title>Mounting</title>
420 <body>
422 <p>
423 Now that your partitions are initialized and are housing a filesystem, it is
424 time to mount those partitions. Use the <c>mount</c> command. Don't forget to
425 create the necessary mount directories for every partition you created. As an
426 example we mount the root and boot partition:
427 </p>
429 <pre caption="Mounting partitions">
430 # <i>mount /dev/sda3 /mnt/gentoo</i>
431 # <i>mkdir /mnt/gentoo/boot</i>
432 # <i>mount /dev/sda1 /mnt/gentoo/boot</i>
433 </pre>
435 <note>
436 If you want your <path>/tmp</path> to reside on a separate partition, be sure to
437 change its permissions after mounting: <c>chmod 1777 /mnt/gentoo/tmp</c>. This
438 also holds for <path>/var/tmp</path>.
439 </note>
441 <p>
442 We will also have to mount the proc filesystem (a virtual interface with the
443 kernel) on <path>/proc</path>. But first we will need to place our files on the partitions.
444 </p>
446 <p>
447 Continue with <uri link="?part=1&amp;chap=5">Installing the Gentoo
448 Installation Files</uri>.
449 </p>
451 </body>
452 </section>
453 </sections>

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