From 943088df2c3317ff7d4e5b5e1c759ddb397f7b20 Mon Sep 17 00:00:00 2001
From: Alf Mikula <amikula@gmail.com>
Date: Tue, 8 Sep 2020 06:49:35 -0700
Subject: [PATCH] Keep oldest archive when retention target is not met

---
 src/borg/helpers/misc.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/borg/helpers/misc.py b/src/borg/helpers/misc.py
index 3e62b3e4a..ea8655ab5 100644
--- a/src/borg/helpers/misc.py
+++ b/src/borg/helpers/misc.py
@@ -58,6 +58,10 @@ def prune_split(archives, rule, n, kept_because=None):
                 kept_because[a.id] = (rule, len(keep))
                 if len(keep) == n:
                     break
+    # Keep oldest archive if we didn't reach the target retention count
+    if len(keep) < n and a.id not in kept_because:
+        keep.append(a)
+        kept_because[a.id] = (rule+"[oldest]", len(keep))
     return keep