22:
152:(FIFO) backup scheme saves new or modified files onto the "oldest" media in the set, i.e. the media that contain the oldest and thus least useful previously backed up data. Performing a daily backup onto a set of 14 media, the backup depth would be 14 days. Each day, the oldest media would be inserted when performing the backup. This is the simplest rotation scheme and is usually the first to come to mind.
1191:(Version 2.0 ed.). Ithaca, NY: TidBITS Electronic Publishing. pp. 18-20 (The Archive), 24 (client-server), 82-83 (archive file), 112-114 (Off-site storage backup rotation scheme), 126-141 (old Retrospect terminology and GUI—still used in Windows variant), 165 (client-server), 128 (subvolume—later renamed Favorite Folder in Macintosh variant).
1145:
This method has many variations and names. A set of numbered media is used until the end of the cycle. Then the cycle is repeated using media numbered the same as the previous cycle, but incremented by one. The lowest numbered tape from the previous cycle is retired and kept permanently. Thus one has
168:
Grandfather-father-son backup (GFS) is a common rotation scheme for backup media, in which there are three or more backup cycles, such as daily, weekly and monthly. The daily backups are rotated on a 3-months basis using a FIFO system as above. The weekly backups are similarly rotated on a bi-yearly
159:
However, this scheme suffers from the possibility of data loss: suppose, an error is introduced into the data, but the problem is not identified until several generations of backups and revisions have taken place. Thus when the error is detected, all the backup files contain the error. It would then
181:
puzzle, using a recursive method to optimize the back-up cycle. Every tape corresponds to a disk in the puzzle, and every disk movement to a different peg corresponds with a backup to that tape. So the first tape is used every other day (1, 3, 5, 7, 9, ...), the second tape is used every fourth day
130:) that minimizes, by re-use, the number of media used. The scheme determines how and when each piece of removable storage is used for a backup job and how long it is retained once it has backup data stored on it. Different techniques have evolved over time to balance
155:
This scheme has the advantage that it retains the longest possible tail of daily backups. It can be used when archived data is unimportant (or is retained separately from the short-term backup data) and data before the rotation period is irrelevant.
169:
basis, and the monthly backup on a yearly basis. In addition, quarterly, half-yearly, and/or annual backups could also be separately retained. Often some of these backups are removed from the site for safekeeping and disaster recovery purposes.
1133:
of generations, whereas a smaller exponent leads to a distribution with more recent and fewer older generations. This technique probabilistically ensures that past generations are always distributed across all points in time as is desired.
134:
and restoration needs with the cost of extra data storage media. Such a scheme can be quite complicated if it takes incremental backups, multiple retention periods, and off-site storage into consideration.
1146:
access to every backup for one cycle and to one backup per cycle before that. This method has the advantage of ensuring even media wear, but requires a schedule to be precalculated.
1110:
generations) when necessary in a weighted-random fashion. For each deletion, the weight assigned to each deletable generation corresponds to the probability of it being deleted.
1106:
An alternative arrangement is to keep generations distributed across all points in time is by deleting (or overwriting) past generations (except the oldest and the most-recent-
1035:
And Tower of Hanoi has the huge advantage of freeing implementers from having to deal with managing hourly, daily, weekly, monthly, quarterly or annual management strategies.
203:
The following tables show which tapes are used on which days of various cycles. A disadvantage of the method is that half the backups are overwritten after only two days.
1129:
of the duration (possibly expressed in the number of days) between the dates of the generation and the generation preceding it. Using a larger exponent leads to a more
1183:
1032:
Coverage automatically gets sparser the further back in time one goes, which approximates the likelihood of needing to do restores from past backups.
192:(or other media) will allow backups for 2 days before the last set is recycled. So, 3 tapes will give 4 days' worth of backups, and on the 4th day
1018:
Many variations are possible, and the concepts are readily extended to disc-based directories containing backups. Here are some options:
86:
58:
39:
65:
1266:
1202:
200:
is overwritten on the 9th day; 5 tapes will give 16 days, etc. Files can be restored from 1, 2, 4, 8, 16, ..., 2 days ago.
1137:
The weighted random method only has an advantage over a more systematic approach, when backups are irregular or missed.
72:
1196:
105:
149:
54:
1130:
43:
1057:
Here is an example showing coverage, including set 0, keeping at least the last 4 days, and recycling:
189:
127:
79:
1155:
32:
1241:
1126:
177:
The Tower of Hanoi rotation method is more complex. It is based on the mathematics of the
160:
be useful to have at least one older version of the data, as it would not have the error.
8:
1192:
1054:
is the sequence or serial number of a backup (also the Tower of Hanoi move number).
1122:
1271:
1114:
1118:
178:
131:
1260:
1220:
182:(2, 6, 10, ...), the third tape is used every eighth day (4, 12, 20, ...).
1160:
21:
123:
1218:
1028:
Save more than one of each set number, for greater coverage.
1177:
1175:
1172:
1239:
1025:
Save as many of the most recent backups as desired.
196:will be overwritten; 4 tapes will give 8 days, and
46:. Unsourced material may be challenged and removed.
1258:
1101:
1219:San Francisco Computer Repair (2008-01-13).
206:
1140:
534:
313:
1013:
163:
106:Learn how and when to remove this message
1085:precious.20160618.seq.737.recycle set 1
1259:
143:
44:adding citations to reliable sources
15:
1242:"Tower of Hanoi pattern for backup"
13:
1240:Alvechurch Data Ltd (2007-11-27).
14:
1283:
172:
1185:Take Control of Mac OS X Backups
1067:precious.20151026.seq.512 set 10
126:data to computer media (such as
20:
1097:precious.20160622.seq.741 set 1
1094:precious.20160621.seq.740 set 3
1091:precious.20160620.seq.739 set 1
1088:precious.20160619.seq.738 set 2
1082:precious.20160617.seq.736 set 6
1079:precious.20160609.seq.728 set 4
1076:precious.20160601.seq.720 set 5
1073:precious.20160516.seq.704 set 7
1070:precious.20160311.seq.640 set 8
1064:precious.20150205.seq.256 set 9
1022:Save a base backup as set zero.
31:needs additional citations for
1233:
1212:
1182:Kissell, Joe (February 2007).
1038:In general, backup set number
1:
1166:
1061:precious.20140515.seq.0 set 0
1181:
1102:Weighted random distribution
1050:= 0, 1, 2, 3, 4, ..., where
7:
1267:Tape-based computer storage
1149:
10:
1288:
543:
322:
138:
646:
541:
377:
320:
246:
215:
213:
207:Three-tape Hanoi schedule
1156:Off-site data protection
1141:Incremented media method
535:Five-tape Hanoi schedule
314:Four-tape Hanoi schedule
55:"Backup rotation scheme"
1127:multiplicative inverse
1014:Extensions and example
164:Grandfather-father-son
120:backup rotation scheme
1131:uniform distribution
40:improve this article
150:first in, first out
144:First in, first out
1011:
1010:
544:Day of the cycle
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323:Day of the cycle
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216:Day of the cycle
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90:
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1221:"Backup Methods"
1216:
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1201:. Archived from
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1113:One acceptable
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122:is a system of
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1208:on 2018-10-15.
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1121:(possibly the
1117:is a constant
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179:Tower of Hanoi
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132:data retention
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1198:0-9759503-0-4
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1046:= 2 + j × 2,
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57: –
56:
52:
51:Find sources:
45:
41:
35:
34:
29:This article
27:
23:
18:
17:
1245:. Retrieved
1235:
1224:. Retrieved
1214:
1203:the original
1184:
1144:
1136:
1112:
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96:January 2010
93:
83:
76:
69:
62:
50:
38:Please help
33:verification
30:
1042:is used at
1261:Categories
1247:2008-03-12
1226:2008-02-21
1167:References
1161:Legal hold
124:backing up
66:newspapers
1125:) of the
185:A set of
1150:See also
1119:exponent
139:Schemes
80:scholar
1272:Backup
1195:
1123:square
1115:weight
82:
75:
68:
61:
53:
1206:(PDF)
1189:(PDF)
198:Set D
194:Set C
190:tapes
128:tapes
87:JSTOR
73:books
1193:ISBN
647:Set
378:Set
247:Set
59:news
1052:seq
1044:seq
1040:set
642:32
639:31
636:30
633:29
630:28
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233:05
230:04
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224:02
221:01
42:by
1263::
1174:^
1007:E
974:E
923:D
890:D
863:C
846:C
829:C
812:C
797:B
788:B
779:B
770:B
761:B
752:B
743:B
734:B
725:A
720:A
715:A
710:A
705:A
700:A
695:A
690:A
685:A
680:A
675:A
670:A
665:A
660:A
655:A
650:A
528:D
511:D
484:C
467:C
452:B
443:B
434:B
425:B
416:A
411:A
406:A
401:A
396:A
391:A
386:A
381:A
307:C
298:C
283:B
274:B
265:A
260:A
255:A
250:A
148:A
118:A
1250:.
1229:.
1108:n
1048:j
187:n
109:)
103:(
98:)
94:(
84:·
77:·
70:·
63:·
36:.
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
