+int typestr="days"
+default="4"
+optional
+details="
+ 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.
+"