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129 lines
5.5 KiB
Text
129 lines
5.5 KiB
Text
borg prune visualized
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=====================
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Assume it is 2016-01-01. Today's archive has not yet been made. You have
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created at least one archive on each day in 2015 except on 2015-12-19 (no
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backup was made on that day), and you started backing up with Borg on
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2015-01-01.
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This is what borg prune --keep-daily 14 --keep-monthly 6 --keep-yearly 1
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would keep.
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Archives kept by the --keep-daily rule are marked by a "d" to the right,
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archives kept by the --keep-monthly rule are marked by a "m" to the right, and
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archives kept by the --keep-yearly rule are marked by a "y" to the right.
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Calendar view
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-------------
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2015
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January February March
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Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su
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1y 2 3 4 1 1
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5 6 7 8 9 10 11 2 3 4 5 6 7 8 2 3 4 5 6 7 8
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12 13 14 15 16 17 18 9 10 11 12 13 14 15 9 10 11 12 13 14 15
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19 20 21 22 23 24 25 16 17 18 19 20 21 22 16 17 18 19 20 21 22
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26 27 28 29 30 31 23 24 25 26 27 28 23 24 25 26 27 28 29
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30 31
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April May June
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Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su
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1 2 3 4 5 1 2 3 1 2 3 4 5 6 7
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6 7 8 9 10 11 12 4 5 6 7 8 9 10 8 9 10 11 12 13 14
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13 14 15 16 17 18 19 11 12 13 14 15 16 17 15 16 17 18 19 20 21
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20 21 22 23 24 25 26 18 19 20 21 22 23 24 22 23 24 25 26 27 28
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27 28 29 30 25 26 27 28 29 30 31 29 30m
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July August September
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Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su
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1 2 3 4 5 1 2 1 2 3 4 5 6
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6 7 8 9 10 11 12 3 4 5 6 7 8 9 7 8 9 10 11 12 13
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13 14 15 16 17 18 19 10 11 12 13 14 15 16 14 15 16 17 18 19 20
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20 21 22 23 24 25 26 17 18 19 20 21 22 23 21 22 23 24 25 26 27
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27 28 29 30 31m 24 25 26 27 28 29 30 28 29 30m
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31m
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October November December
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Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su
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1 2 3 4 1 1 2 3 4 5 6
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5 6 7 8 9 10 11 2 3 4 5 6 7 8 7 8 9 10 11 12 13
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12 13 14 15 16 17 18 9 10 11 12 13 14 15 14 15 16 17d18d19 20d
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19 20 21 22 23 24 25 16 17 18 19 20 21 22 21d22d23d24d25d26d27d
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26 27 28 29 30 31m 23 24 25 26 27 28 29 28d29d30d31d
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30m
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List view
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---------
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--keep-daily 14 --keep-monthly 6 --keep-yearly 1
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----------------------------------------------------------------
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1. 2015-12-31 (2015-12-31 kept (2015-12-31 kept
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2. 2015-12-30 by daily rule) by daily rule)
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3. 2015-12-29 1. 2015-11-30 1. 2015-01-01 (oldest)
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4. 2015-12-28 2. 2015-10-31
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5. 2015-12-27 3. 2015-09-30
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6. 2015-12-26 4. 2015-08-31
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7. 2015-12-25 5. 2015-07-31
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8. 2015-12-24 6. 2015-06-30
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9. 2015-12-23
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10. 2015-12-22
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11. 2015-12-21
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12. 2015-12-20
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(no archive made on 2015-12-19)
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13. 2015-12-18
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14. 2015-12-17
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Notes
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-----
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2015-12-31 is kept due to the --keep-daily 14 rule (because it is applied
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first), not due to the --keep-monthly or --keep-yearly rule.
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Rules are applied in the order given: archives already kept by an earlier
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rule are excluded from consideration by later rules.
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The --keep-yearly 1 rule does not consider the December 31st archive because it
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has already been kept due to the daily rule. There are no archives from
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previous years, so there are no "true" yearly candidates. The oldest archive at
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2015-01-01 fills the remaining slot and will be kept until the rolling backup
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scheme reaches "steady state" (when all retention rules are fully satisfied).
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The --keep-monthly 6 rule keeps Nov, Oct, Sep, Aug, Jul and Jun. December is
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not considered for this rule, because that archive was already kept because of
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the daily rule.
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2015-12-17 is kept to satisfy the --keep-daily 14 rule, because no archive was
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made on 2015-12-19. If an archive had been made on that day, it would not keep
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the archive from 2015-12-17.
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We did not include weekly, hourly, minutely, or secondly rules to keep this
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example simple. They all work in basically the same way.
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The weekly rule is easy to understand roughly, but hard to understand in all
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details. If you are interested, read "ISO 8601:2000 standard week-based year".
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The 13weekly and 3monthly rules are two different strategies for keeping one
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archive every quarter of a year. There are `multiple ways` to define a
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quarter-year; borg prune recognizes two:
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* --keep-13weekly keeps one archive every 13 weeks using ISO 8601:2000's
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definition of the week-based year. January 4th is always included in the
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first week of a year, and January 1st to 3rd may be in week 52 or 53 of the
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previous year. Week 53 is also in the fourth quarter of the year.
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* --keep-3monthly keeps one archive every 3 months. January 1st to March 31,
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April 1st to June 30th, July 1st to September 30th, and October 1st to
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December 31st form the quarters.
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If the subtleties of the definition of a quarter-year don't matter to you, a
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short summary of behavior is:
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* --keep-13weekly favors keeping archives at the beginning of Jan, Apr, Jul,
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and Oct.
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* --keep-3monthly favors keeping archives at the end of Dec, Mar, Jun, and Sep.
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* Both strategies will have some overlap in which archives are kept.
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* The differences are negligible unless archives considered for deletion were
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created weekly or more frequently.
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.. _multiple ways: https://en.wikipedia.org/wiki/Calendar_year#Quarter_year
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