1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
|
<!DOCTYPE HTML PUBLIC "-//Norman Walsh//DTD DocBook HTML 1.0//EN">
<HTML
><HEAD
><TITLE
>Multilevel backups</TITLE
><META
NAME="GENERATOR"
CONTENT="Modular DocBook HTML Stylesheet"><LINK
REL="HOME"
TITLE="The Linux System Administrators' Guide"
HREF="book1.html"><LINK
REL="UP"
TITLE="Backups"
HREF="c2187.html"><LINK
REL="PREVIOUS"
TITLE="Simple backups"
HREF="x2240.html"><LINK
REL="NEXT"
TITLE="What to back up"
HREF="x2405.html"></HEAD
><BODY
BGCOLOR="#FFFFFF"
TEXT="#000000"
><DIV
CLASS="NAVHEADER"
><TABLE
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TH
COLSPAN="3"
ALIGN="center"
>The Linux System Administrators' Guide</TH
></TR
><TR
><TD
WIDTH="10%"
ALIGN="left"
VALIGN="bottom"
><A
HREF="x2240.html"
>Prev</A
></TD
><TD
WIDTH="80%"
ALIGN="center"
VALIGN="bottom"
>Chapter 10. Backups</TD
><TD
WIDTH="10%"
ALIGN="right"
VALIGN="bottom"
><A
HREF="x2405.html"
>Next</A
></TD
></TR
></TABLE
><HR
ALIGN="LEFT"
WIDTH="100%"></DIV
><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="AEN2315"
>Multilevel backups</A
></H1
><P
> The simple backup method outlined in the previous section
is often quite adequate for personal use or small sites. For more
heavy duty use, multilevel backups are more appropriate. </P
><P
> The simple method has two backup levels: full and
incremental backups. This can be generalized to any number of
levels. A full backup would be level 0, and the different levels
of incremental backups levels 1, 2, 3, etc. At each incremental
backup level you back up everything that has changed since the
previous backup at the same or a previous level. </P
><P
> The purpose for doing this is that it allows a longer
<I
CLASS="GLOSSTERM"
>backup history</I
> cheaply. In the example in
the previous section, the backup history went back to the previous
full backup. This could be extended by having more tapes, but
only a week per new tape, which might be too expensive. A longer
backup history is useful, since deleted or corrupted files are
often not noticed for a long time. Even a version of a file that
is not very up to date is better than no file at all. </P
><P
> With multiple levels the backup history can be extended
more cheaply. For example, if we buy ten tapes, we could use
tapes 1 and 2 for monthly backups (first Friday each month),
tapes 3 to 6 for weekly backups (other Fridays; note that there
can be five Fridays in one month, so we need four more tapes),
and tapes 7 to 10 for daily backups (Monday to Thursday).
With only four more tapes, we've been able to extend the backup
history from two weeks (after all daily tapes have been used)
to two months. It is true that we can't restore every version
of each file during those two months, but what we can restore
is often good enough. </P
><P
><A
HREF="x2315.html#BACKUP-HISTORY-TIMELINE"
>Figure 10-1</A
> shows which backup
level is used each day, and which backups can be restored from
at the end of the month. </P
><DIV
CLASS="FIGURE"
><P
><B
><A
NAME="BACKUP-HISTORY-TIMELINE"
>Figure 10-1. A sample multilevel backup schedule.</A
></B
></P
><P
><IMG
SRC="backup-timeline.gif"></P
></DIV
><P
> Backup levels can also be used to keep filesystem
restoration time to a minimum. If you have many incremental
backups with monotonously growing level numbers, you need to
restore all of them if you need to rebuild the whole filesystem.
Instead you can use level numbers that aren't monotonous, and
keep down the number of backups to restore. </P
><P
> To minimize the number of tapes needed to restore, you
could use a smaller level for each incremental tape. However,
then the time to make the backups increases (each backup copies
everything since the previous full backup). A better scheme is
suggested by the <B
CLASS="COMMAND"
>dump</B
> manual page and described
by the table XX (efficient-backup-levels). Use the following
succession of backup levels: 3, 2, 5, 4, 7, 6, 9, 8, 9, etc.
This keeps both the backup and restore times low. The most you
have to backup is two day's worth of work. The number of tapes
for a restore depends on how long you keep between full backups,
but it is less than in the simple schemes. </P
><DIV
CLASS="TABLE"
><P
><B
><A
NAME="EFFICIENT-BACKUP-LEVELS"
>Table 10-1. Efficient backup scheme using many backup levels</A
></B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><TR
><TH
ALIGN="LEFT"
VALIGN="TOP"
>Tape</TH
><TH
ALIGN="LEFT"
VALIGN="TOP"
>Level</TH
><TH
ALIGN="LEFT"
VALIGN="TOP"
>Backup (days)</TH
><TH
ALIGN="LEFT"
VALIGN="TOP"
>Restore tapes</TH
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>1</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>0</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>n/a</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>1</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>2</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>3</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>1</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>1, 2</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>3</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>2</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>2</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>1, 3</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>4</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>5</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>1</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>1, 2, 4</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>5</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>4</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>2</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>1, 2, 5</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>6</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>7</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>1</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>1, 2, 5, 6</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>7</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>6</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>2</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>1, 2, 5, 7</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>8</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>9</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>1</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>1, 2, 5, 7, 8</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>9</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>8</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>2</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>1, 2, 5, 7, 9</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>10</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>9</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>1</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>1, 2, 5, 7, 9, 10</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>11</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>9</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>1</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>1, 2, 5, 7, 9, 10, 11</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
>...</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>9</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>1</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>1, 2, 5, 7, 9, 10, 11, ...</TD
></TR
></TABLE
></DIV
><P
> A fancy scheme can reduce the amount of labor needed, but
it does mean there are more things to keep track of. You must
decide if it is worth it. </P
><P
> <B
CLASS="COMMAND"
>dump</B
> has built-in support for backup
levels. For <B
CLASS="COMMAND"
>tar</B
> and <B
CLASS="COMMAND"
>cpio</B
>
it must be implemented with shell scripts. </P
></DIV
><DIV
CLASS="NAVFOOTER"
><HR
ALIGN="LEFT"
WIDTH="100%"><TABLE
WIDTH="100%"
BORDER="0"
CELLPADDING="0"
CELLSPACING="0"
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
><A
HREF="x2240.html"
>Prev</A
></TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="book1.html"
>Home</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
><A
HREF="x2405.html"
>Next</A
></TD
></TR
><TR
><TD
WIDTH="33%"
ALIGN="left"
VALIGN="top"
>Simple backups</TD
><TD
WIDTH="34%"
ALIGN="center"
VALIGN="top"
><A
HREF="c2187.html"
>Up</A
></TD
><TD
WIDTH="33%"
ALIGN="right"
VALIGN="top"
>What to back up</TD
></TR
></TABLE
></DIV
></BODY
></HTML
>
|
