diff --git a/redmine-files-backup/redmine-files-backup.sh b/redmine-files-backup/redmine-files-backup.sh
index 8d45e11..84d2c2e 100644
--- a/redmine-files-backup/redmine-files-backup.sh
+++ b/redmine-files-backup/redmine-files-backup.sh
@@ -4,13 +4,13 @@ set -euo pipefail
 SRC="/opt/redmine/redmine_files"
 BASE="/var/backups/tscale01/redmine_files"
 PREFIX="redmine_files"
-RETENTION_DAYS=3
-
-TIMESTAMP="$(date '+%Y%m%d_%H%M%S')"
-DEST="${BASE}/${PREFIX}-${TIMESTAMP}"
+KEEP=3
 
 LOG="/var/log/backup-redmine-files.log"
-LOCK="/var/lock/backup-redmine-files.lock"
+LOCK="/var/lock/redmine-files-backup.lock"
+
+timestamp="$(date '+%Y%m%d_%H%M%S')"
+DEST="${BASE}/${PREFIX}-${timestamp}"
 
 log() {
     printf "%s %s\n" "$(date '+%Y-%m-%d %H:%M:%S')" "$1" | tee -a "$LOG"
@@ -21,11 +21,15 @@ cleanup() {
 }
 trap cleanup EXIT
 
+# Lock semplice
 if ! ( set -o noclobber; echo "$$" > "$LOCK" ) 2>/dev/null; then
     log "ERRORE: un'altra istanza è in esecuzione."
     exit 1
 fi
 
+# Verifiche base
+[ -d "$SRC" ] || { log "ERRORE: sorgente $SRC inesistente"; exit 1; }
+mkdir -p "$BASE"
 mkdir -p "$DEST"
 
 log "Inizio snapshot → $DEST"
@@ -34,10 +38,19 @@ rsync -a --delete "$SRC"/ "$DEST"/
 
 log "Snapshot completato."
 
-log "Avvio retention (ultimi $RETENTION_DAYS giorni)…"
+# Retention per numero: tieni gli ultimi $KEEP, cancella il resto
+log "Avvio retention: mantengo ultimi $KEEP snapshot."
 
-find "$BASE" -maxdepth 1 -type d -name "${PREFIX}-*" \
-    -mtime +"$RETENTION_DAYS" -print -exec rm -rf {} \;
+# Lista directory in ordine dal più recente al più vecchio
+snapshots=( $(ls -1dt "${BASE}/${PREFIX}-"* 2>/dev/null || true) )
+
+if [ "${#snapshots[@]}" -gt "$KEEP" ]; then
+    to_delete=( "${snapshots[@]:$KEEP}" )
+    for dir in "${to_delete[@]}"; do
+        log "Elimino snapshot vecchio: $dir"
+        rm -rf -- "$dir"
+    done
+fi
 
 log "Retention completata."
 exit 0