- dss snapshot aging is implemented in terms of intervals. There are
- two command line options related to intervals: the duration of a
- \"unit\" interval and the number of those unit intervals.
-
- dss removes any snapshots older than the given number of intervals
- times the duration of an unit interval and tries to keep the following
- number of snapshots per interval:
-
- interval number number of snapshots
- ===============================================
- 0 2 ^ (num-intervals - 1)
- 1 2 ^ (num-intervals - 2)
- 2 2 ^ (num-intervals - 3)
- ...
- num-intervals - 2 2
- num-intervals - 1 1
- num-intervals 0
-
- In other words, the oldest snapshot will at most be unit_interval *
- num_intervals old (= 5 days * 4 = 20 days if default values are used).
- Moreover, there are at most 2^num_intervals - 1 snapshots in total
- (i.e. 31 by default). Observe that you have to create at least
- 2 ^ (num_intervals - 1) snapshots each interval for this to work out.
+ dss snapshot aging is implemented in terms of intervals. There
+ are two command line options related to intervals: the
+ duration u of a \"unit\" interval and the number n of those
+ unit intervals.
+
+ dss removes any snapshots older than n times u and tries to
+ keep 2^(n - k - 1) snapshots in interval k, where the interval
+ number k counts from zero, zero being the most recent unit
+ interval.
+
+ In other words, the oldest snapshot will at most be u * n days
+ (= 20 days if default values are used) old. Moreover, there
+ are at most 2^n - 1 snapshots in total (i. e. 31 by default).
+ Observe that you have to create at least 2^(n - 1) snapshots
+ each interval for this to work out because that is the number
+ of snapshots in interval zero.