+.B "\-\-reduce-device-size \fInumber of 512 bytes sectors\fR"
+Enlarge data offset for specified value of sectors by shrinking
+device size.
+
+This means that last sectors on the original device will be lost,
+ciphertext data will be effectively shifted by specified
+number of sectors.
+
+It can be usefull if you e.g. added some space to underlying
+partition (so last sectors contains no data).
+
+WARNING: This is destructive operation and cannot be reverted.
+Use with extreme care - shrinked filesystems are usually unrecoverable.
+
+You cannot shrink device more than by 64 MiB (131072 sectors).
+.TP