diff --git a/libraries/DataFlash/DataFlash_File.cpp b/libraries/DataFlash/DataFlash_File.cpp
index cfc4a7c246..abab630603 100644
--- a/libraries/DataFlash/DataFlash_File.cpp
+++ b/libraries/DataFlash/DataFlash_File.cpp
@@ -56,6 +56,7 @@ DataFlash_File::DataFlash_File(DataFlash_Class &front, const char *log_directory
     _initialised(false),
     _open_error(false),
     _log_directory(log_directory),
+    _cached_oldest_log(0),
     _writebuf(NULL),
     _writebuf_size(16*1024),
 #if defined(CONFIG_ARCH_BOARD_PX4FMU_V1)
@@ -229,6 +230,10 @@ float DataFlash_File::avail_space_percent()
 // returns 0 if no log was found
 uint16_t DataFlash_File::find_oldest_log()
 {
+    if (_cached_oldest_log != 0) {
+        return _cached_oldest_log;
+    }
+
     uint16_t last_log_num = find_last_log();
     if (last_log_num == 0) {
         return 0;
@@ -281,6 +286,7 @@ uint16_t DataFlash_File::find_oldest_log()
         }
     }
     closedir(d);
+    _cached_oldest_log = current_oldest_log;
 
     return current_oldest_log;
 }
@@ -293,6 +299,8 @@ void DataFlash_File::Prep_MinSpace()
         return;
     }
 
+    _cached_oldest_log = 0;
+
     uint16_t log_to_remove = first_log_to_remove;
 
     uint16_t count = 0;
@@ -407,6 +415,8 @@ void DataFlash_File::EraseAll()
         unlink(fname);
         free(fname);
     }
+
+    _cached_oldest_log = 0;
 }
 
 /* Write a block of data at current offset */
@@ -584,7 +594,7 @@ void DataFlash_File::get_log_boundaries(const uint16_t list_entry, uint16_t & st
 }
 
 /*
-  find the number of pages in a log
+  retrieve data from a log file
  */
 int16_t DataFlash_File::get_log_data(const uint16_t list_entry, const uint16_t page, const uint32_t offset, const uint16_t len, uint8_t *data)
 {
@@ -738,6 +748,8 @@ uint16_t DataFlash_File::start_new_log(void)
     }
     char *fname = _log_file_name(log_num);
     _write_fd = ::open(fname, O_WRONLY|O_CREAT|O_TRUNC, 0666);
+    _cached_oldest_log = 0;
+
     if (_write_fd == -1) {
         _initialised = false;
         _open_error = true;
diff --git a/libraries/DataFlash/DataFlash_File.h b/libraries/DataFlash/DataFlash_File.h
index d7497e0701..f452b2b05e 100644
--- a/libraries/DataFlash/DataFlash_File.h
+++ b/libraries/DataFlash/DataFlash_File.h
@@ -65,6 +65,8 @@ private:
     volatile bool _open_error;
     const char *_log_directory;
 
+    uint16_t _cached_oldest_log;
+
     /*
       read a block
     */