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1 <?xml version='1.0' encoding='UTF-8'?>
2 <!DOCTYPE sections SYSTEM "/dtd/book.dtd">
3
4 <!-- The content of this document is licensed under the CC-BY-SA license -->
5 <!-- See http://creativecommons.org/licenses/by-sa/1.0 -->
6
7 <!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/handbook/hb-install-mips-disk.xml,v 1.5 2004/08/29 12:17:07 swift Exp $ -->
8
9 <sections>
10 <section>
11 <title>Introduction to Block Devices</title>
12 <subsection>
13 <title>Block Devices</title>
14 <body>
15
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>
23
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>
29
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>
37
38 </body>
39 </subsection>
40 <subsection>
41 <title>Partitions</title>
42 <body>
43
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>
50
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>
59
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>
71
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>
76
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>
95
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. There is also a 15-partition
100 limit for SCSI and SATA.
101 </p>
102
103 </body>
104 </subsection>
105 </section>
106 <section>
107 <title>Using fdisk on MIPS to Partition your Disk</title>
108 <subsection>
109 <title>Creating an SGI Disk Label</title>
110 <body>
111
112 <p>
113 All disks in an SGI System require an <e>SGI Disk Label</e>, which serves a
114 similar function as Sun &amp; MS-DOS disklabels -- It stores information about
115 the disk partitions. Creating a new SGI Disk Label will create two special
116 partitions on the disk:
117 </p>
118
119 <ul>
120 <li>
121 <e>SGI Volume Header</e> (9th partition): This partition is important. It
122 is where the kernel images will go. To store kernel images, you will utilize
123 the tool known as <c>dvhtool</c> to copy kernel images to this partition.
124 You will then be able to boot kernels from this partition via the SGI PROM
125 Monitor.
126 </li>
127 <li>
128 <e>SGI Volume</e> (11th partition): This partition is similar in purpose to
129 the Sun Disklabel's third partition of "Whole Disk". This partition spans
130 the entire disk, and should be left untouched. It serves no special purpose
131 other than to assist the PROM in some undocumented fashion (or it is used by
132 IRIX in some way).
133 </li>
134 </ul>
135
136 <warn>
137 The SGI Volume Header <e>must</e> begin at cylinder 0. Failure to do so means
138 you won't be able to boot from the disk.
139 </warn>
140
141 <p>
142 The following is an example excerpt from an <c>fdisk</c> session. Read and
143 tailor it to your needs...
144 </p>
145
146 <pre caption="Creating an SGI Disklabel">
147 # <i>fdisk /dev/sda</i>
148
149 Command (m for help): <i>x</i>
150
151 Expert command (m for help): <i>m</i>
152 Command action
153 b move beginning of data in a partition
154 c change number of cylinders
155 d print the raw data in the partition table
156 e list extended partitions
157 f fix partition order
158 g create an IRIX (SGI) partition table
159 h change number of heads
160 m print this menu
161 p print the partition table
162 q quit without saving changes
163 r return to main menu
164 s change number of sectors/track
165 v verify the partition table
166 w write table to disk and exit
167
168 Expert command (m for help): <i>g</i>
169 Building a new SGI disklabel. Changes will remain in memory only,
170 until you decide to write them. After that, of course, the previous
171 content will be unrecoverably lost.
172
173 Expert command (m for help): <i>r</i>
174
175 Command (m for help): <i>p</i>
176
177 Disk /dev/sda (SGI disk label): 64 heads, 32 sectors, 17482 cylinders
178 Units = cylinders of 2048 * 512 bytes
179
180 ----- partitions -----
181 Pt# Device Info Start End Sectors Id System
182 9: /dev/sda1 0 4 10240 0 SGI volhdr
183 11: /dev/sda2 0 17481 35803136 6 SGI volume
184 ----- Bootinfo -----
185 Bootfile: /unix
186 ----- Directory Entries -----
187
188 Command (m for help):
189 </pre>
190
191 <note>
192 If your disk already has an existing SGI Disklabel, then fdisk will not allow
193 the creation of a new label. There are two ways around this. One is to create a
194 Sun or MS-DOS disklabel, write the changes to disk, and restart fdisk. The
195 second is to overwrite the partition table with null data via the following
196 command: <c>dd if=/dev/zero of=/dev/sda bs=512 count=1</c>.
197 </note>
198
199 </body>
200 </subsection>
201 <subsection>
202 <title>Getting the SGI Volume Header to just the right size</title>
203 <body>
204
205 <p>
206 Now that an SGI Disklabel is created, partitions may now be defined. In the
207 above example, there are already two partitions defined for you. These are the
208 special partitions mentioned above and should not normally be altered. However,
209 for installing Gentoo, we'll need to load multiple kernel images directly into
210 the volume header, as there is no supported SGI Bootloader available in Portage
211 yet. The volume header itself can hold up to <e>eight</e> images of any size,
212 with each image allowed eight-character names.
213 </p>
214
215 <p>
216 The process of making the volume header larger isn't exactly straight-forward --
217 there's a bit of a trick to it. One cannot simply delete and re-add the volume
218 header due to odd fdisk behavior. In the example provided below, we'll create a
219 50MB Volume header in conjunction with a 50MB /boot partition. The actual layout
220 of your disk may vary, but this is for illustrative purposes only.
221 </p>
222
223 <pre caption="Resizing the SGI Volume Header correctly">
224 Command (m for help): <i>n</i>
225 Partition number (1-16): <i>1</i>
226 First cylinder (5-8682, default 5): <i>51</i>
227 Last cylinder (51-8682, default 8682): <i>101</i>
228 <comment>(Notice how fdisk only allows Partition #1 to be re-created starting at a minimum of cylinder 5)</comment>
229 <comment>(Had you attempted to delete &amp; re-create the SGI Volume Header this way, this is the same issue
230 you would have encountered.)</comment>
231 <comment>(In our example, we want /boot to be 50MB, so we start it at cylinder 51 (the Volume Header needs to
232 start at cylinder 0, remember?), and set its ending cylinder to 101, which will roughly be 50MB (+/- 1-5MB))</comment>
233
234 Command (m for help): <i>d</i>
235 Partition number (1-16): <i>9</i>
236 <comment>(Delete Partition #9 (SGI Volume Header))</comment>
237
238 Command (m for help): <i>n</i>
239 Partition number (1-16): <i>9</i>
240 First cylinder (0-50, default 0): <i>0</i>
241 Last cylinder (0-50, default 50): <i>50</i>
242 <comment>(Re-Create Partition #9, ending just before Partition #1)</comment>
243 </pre>
244
245 </body>
246 </subsection>
247 <subsection>
248 <title>Final partition layout</title>
249 <body>
250
251 <p>
252 Once this is done, you are safe to create the rest of your partitions as you see
253 fit. After all your partitions are laid out, make sure you set the partition ID
254 of your swap partition to <c>82</c>, which is Linux Swap. By default, it will be
255 <c>83</c>, Linux Native.
256 </p>
257
258 <p>
259 Now that your partitions are created, you can now continue with <uri
260 link="#filesystems">Creating Filesystems</uri>.
261 </p>
262
263 </body>
264 </subsection>
265 </section>
266 <section id="filesystems">
267 <title>Creating Filesystems</title>
268 <subsection>
269 <title>Introduction</title>
270 <body>
271
272 <p>
273 Now that your partitions are created, it is time to place a filesystem on them.
274 If you don't care about what filesystem to choose and are happy with what we use
275 as default in this handbook, continue with <uri
276 link="#filesystems-apply">Applying a Filesystem to a Partition</uri>.
277 Otherwise read on to learn about the available filesystems...
278 </p>
279
280 </body>
281 </subsection>
282 <subsection>
283 <title>Filesystems?</title>
284 <body>
285
286 <p>
287 Several filesystems are available. Ext2 and ext3 are found stable on the
288 MIPS architectures, others are experimental.
289 </p>
290
291 <p>
292 <b>ext2</b> is the tried and true Linux filesystem but doesn't have metadata
293 journaling, which means that routine ext2 filesystem checks at startup time can
294 be quite time-consuming. There is now quite a selection of newer-generation
295 journaled filesystems that can be checked for consistency very quickly and are
296 thus generally preferred over their non-journaled counterparts. Journaled
297 filesystems prevent long delays when you boot your system and your filesystem
298 happens to be in an inconsistent state.
299 </p>
300
301 <p>
302 <b>ext3</b> is the journaled version of the ext2 filesystem, providing metadata
303 journaling for fast recovery in addition to other enhanced journaling modes like
304 full data and ordered data journaling. ext3 is a very good and reliable
305 filesystem. It has an additional hashed b-tree indexing option that enables
306 high performance in almost all situations. In short, ext3 is an excellent
307 filesystem.
308 </p>
309
310 <p>
311 <b>ReiserFS</b> is a B*-tree based filesystem that has very good overall
312 performance and greatly outperforms both ext2 and ext3 when dealing with small
313 files (files less than 4k), often by a factor of 10x-15x. ReiserFS also scales
314 extremely well and has metadata journaling. As of kernel 2.4.18+, ReiserFS is
315 solid and usable as both general-purpose filesystem and for extreme cases such
316 as the creation of large filesystems, the use of many small files, very large
317 files and directories containing tens of thousands of files.
318 </p>
319
320 <p>
321 <b>XFS</b> is a filesystem with metadata journaling which comes with a robust
322 feature-set and is optimized for scalability. We only recommend using this
323 filesystem on Linux systems with high-end SCSI and/or fibre channel storage and
324 an uninterruptible power supply. Because XFS aggressively caches in-transit data
325 in RAM, improperly designed programs (those that don't take proper precautions
326 when writing files to disk and there are quite a few of them) can lose a good
327 deal of data if the system goes down unexpectedly.
328 </p>
329
330 <p>
331 <b>JFS</b> is IBM's high-performance journaling filesystem. It has recently
332 become production-ready and there hasn't been a sufficient track record to
333 comment positively nor negatively on its general stability at this point.
334 </p>
335
336 </body>
337 </subsection>
338 <subsection id="filesystems-apply">
339 <title>Applying a Filesystem to a Partition</title>
340 <body>
341
342 <p>
343 To create a filesystem on a partition or volume, there are tools available for
344 each possible filesystem:
345 </p>
346
347 <table>
348 <tr>
349 <th>Filesystem</th>
350 <th>Creation Command</th>
351 </tr>
352 <tr>
353 <ti>ext2</ti>
354 <ti><c>mke2fs</c></ti>
355 </tr>
356 <tr>
357 <ti>ext3</ti>
358 <ti><c>mke2fs -j</c></ti>
359 </tr>
360 <tr>
361 <ti>reiserfs</ti>
362 <ti><c>mkreiserfs</c></ti>
363 </tr>
364 <tr>
365 <ti>xfs</ti>
366 <ti><c>mkfs.xfs</c></ti>
367 </tr>
368 <tr>
369 <ti>jfs</ti>
370 <ti><c>mkfs.jfs</c></ti>
371 </tr>
372 </table>
373
374 <p>
375 For instance, to have the boot partition (<path>/dev/sda1</path> in our
376 example) in ext2 and the root partition (<path>/dev/sda3</path> in our example)
377 in ext3, you would use:
378 </p>
379
380 <pre caption="Applying a filesystem on a partition">
381 # <i>mke2fs /dev/sda1</i>
382 # <i>mke2fs -j /dev/sda3</i>
383 </pre>
384
385 <p>
386 Now create the filesystems on your newly created partitions (or logical
387 volumes).
388 </p>
389
390 </body>
391 </subsection>
392 <subsection>
393 <title>Activating the Swap Partition</title>
394 <body>
395
396 <p>
397 <c>mkswap</c> is the command that is used to initialize swap partitions:
398 </p>
399
400 <pre caption="Creating a Swap signature">
401 # <i>mkswap /dev/sda2</i>
402 </pre>
403
404 <p>
405 To activate the swap partition, use <c>swapon</c>:
406 </p>
407
408 <pre caption="Activating the swap partition">
409 # <i>swapon /dev/sda2</i>
410 </pre>
411
412 <p>
413 Create and activate the swap now.
414 </p>
415
416 </body>
417 </subsection>
418 </section>
419 <section>
420 <title>Mounting</title>
421 <body>
422
423 <p>
424 Now that your partitions are initialized and are housing a filesystem, it is
425 time to mount those partitions. Use the <c>mount</c> command. Don't forget to
426 create the necessary mount directories for every partition you created. As an
427 example we mount the root and boot partition:
428 </p>
429
430 <pre caption="Mounting partitions">
431 # <i>mount /dev/sda3 /mnt/gentoo</i>
432 # <i>mkdir /mnt/gentoo/boot</i>
433 # <i>mount /dev/sda1 /mnt/gentoo/boot</i>
434 </pre>
435
436 <note>
437 If you want your <path>/tmp</path> to reside on a separate partition, be sure to
438 change its permissions after mounting: <c>chmod 1777 /mnt/gentoo/tmp</c>. This
439 also holds for <path>/var/tmp</path>.
440 </note>
441
442 <p>
443 We will also have to mount the proc filesystem (a virtual interface with the
444 kernel) on <path>/proc</path>. But first we will need to place our files on the partitions.
445 </p>
446
447 <p>
448 Continue with <uri link="?part=1&amp;chap=5">Installing the Gentoo
449 Installation Files</uri>.
450 </p>
451
452 </body>
453 </section>
454 </sections>

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