In order to improve the performance and efficient usage of our MARS system, the server produces a warning whenever an inefficient access pattern is detected, eg:
mars - INFO - 20201216.185011 - The efficiency of your requests in the last 12 hours is 14% [marsod-core] mars - WARN - 20201216.185011 - Please see https://confluence.ecmwf.int/x/rxRtD in order to improve the efficiency of your requests [marsod-core]
A typical inefficient request pattern usually involves repeated access to elements of data which are stored in the same file on tape using separate MARS requests. This pattern forces multiple mounts of the tape (which is a very expensive operation for a tape-based mass storage system) that could be avoided if a single combined larger request were to be used.
The efficiency score is the number of unique tape file accessed divided by the number of requests to access these files:
Access 10 files with 10 requests = 100% score
Access 1 file with 10 requests = 10% score
We would recommend you to read Guidelines to write efficient MARS requests, but please do contact us via our support portal if you need any further advice.