# Issues with configuring the UM I/O server **URL:** \ **Category:** Unified Model\ **Tags:** io-server\ **Created:** [27 June 2025 08:19 UTC](https://forum.access-hive.org.au/t/issues-with-configuring-the-um-i-o-server/4653 "2025-06-27T08:19:06Z")\ **Posts on this page:** 1\ **Showing post:** 6
**Author:** ![Paul.Gregory](https://sea2.discourse-cdn.com/flex020/user_avatar/forum.access-hive.org.au/paul.gregory/32/2566_2.png) [@Paul.Gregory](https://forum.access-hive.org.au/u/Paul.Gregory)\ **Post date:** [1 July 2025 11:57 UTC](https://forum.access-hive.org.au/t/issues-with-configuring-the-um-i-o-server/4653/6 "2025-07-01T11:57:40Z")
Thanks to @cbengel for creating a branch of this suite without netCDF outputs, I got the IO server running. The relevant parts of the `umnsa.fort6.pe0` are ```auto FILE_MANAGER: Assigned : pseudo-file for UNIX operations FILE_MANAGER: : id : io_reserved_unit FILE_MANAGER: : Unit : 10 (portio) .... 792 Processors initialised. I am PE 0 on gadi-cpu-clx-1621.gadi.nci.org.au [0] I am running with 2 thread(s). [0] OpenMP Specification: 201611 FILE_MANAGER: Assigned : ATMOSCNTL FILE_MANAGER: : id : atmoscntl FILE_MANAGER: : Unit : 11 (fortran) FILE_MANAGER: Assigned : SHARED FILE_MANAGER: : id : shared FILE_MANAGER: : Unit : 12 (fortran) ... MPPIO_File_Utils: Initialised file utils using unit 10 ... FILE_MANAGER: Assigned : Reserved unit for re-initialised stream (/home/548/pag548/cylc-run/u-dq126/share/cycle/20220226T0000Z/Flags hip_ERA5to1km/12km/GAL9/um//umnsaa_pb%N) FILE_MANAGER: : id : pp1 FILE_MANAGER: : Unit : 11 (portio) FILE_MANAGER: Assigned : Reserved unit for re-initialised stream (/home/548/pag548/cylc-run/u-dq126/share/cycle/20220226T0000Z/Flags hip_ERA5to1km/12km/GAL9/um//umnsaa_pa%N) FILE_MANAGER: : id : pp0 FILE_MANAGER: : Unit : 12 (portio) FILE_MANAGER: Assigned : Reserved unit for re-initialised stream (/home/548/pag548/cylc-run/u-dq126/share/cycle/20220226T0000Z/Flags hip_ERA5to1km/12km/GAL9/um//umnsaa_cb%N) FILE_MANAGER: : id : ppmbc FILE_MANAGER: : Unit : 13 (portio) FILE_MANAGER: Assigned : Reserved unit for re-initialised stream (/home/548/pag548/cylc-run/u-dq126/share/cycle/20220226T0000Z/Flags hip_ERA5to1km/12km/GAL9/um//umnsaa_pvera%N) FILE_MANAGER: : id : verpp1 FILE_MANAGER: : Unit : 14 (portio) FILE_MANAGER: Assigned : Reserved unit for re-initialised stream (/home/548/pag548/cylc-run/u-dq126/share/cycle/20220226T0000Z/Flags hip_ERA5to1km/12km/GAL9/um//umnsaa_pverb%N) FILE_MANAGER: : id : verpp2 FILE_MANAGER: : Unit : 15 (portio) FILE_MANAGER: Assigned : Reserved unit for re-initialised stream (/home/548/pag548/cylc-run/u-dq126/share/cycle/20220226T0000Z/Flags hip_ERA5to1km/12km/GAL9/um//umnsaa_pverc%N) FILE_MANAGER: : id : verpp3 FILE_MANAGER: : Unit : 16 (portio) FILE_MANAGER: Assigned : Reserved unit for re-initialised stream (/home/548/pag548/cylc-run/u-dq126/share/cycle/20220226T0000Z/Flags hip_ERA5to1km/12km/GAL9/um//umnsaa_pverd%N) FILE_MANAGER: : id : verpp4 FILE_MANAGER: : Unit : 17 (portio) ``` So when using field fields, Unit numbers 11 to 17 are used for outputs. I’ll now proceed to test a larger I/O server on the larger domains to see what the speed-up is. RE : Unit number allocations for netCDF outputs. The `file_manager` module ([https://code.metoffice.gov.uk/trac/um/browser/main/trunk/src/io\_services/model\_api/file\_manager.F90](https://code.metoffice.gov.uk/trac/um/browser/main/trunk/src/io_services/model_api/file_manager.F90)) suggests the units number for file I/O is read from the Fortran derived types ```auto um_file_list % file_unit_min um_file_list % file_unit_max ``` There are three types used for `fortran`, `portio` and `netcdf` filetypes: ```auto 147 ! The instances of the type used as the master list objects by this module, 148 ! there are two distinct file lists depending on the type of file 149 !------------------------------------------------------------------------------- 150 TYPE(um_file_list_type), SAVE, TARGET :: um_file_list_fortran 151 TYPE(um_file_list_type), SAVE, TARGET :: um_file_list_portio 152 TYPE(um_file_list_type), SAVE, TARGET :: um_file_list_netcdf ``` And they are apparently defined here: ```auto 160 INTEGER, PARAMETER :: start_unit_fortran = 10 161 INTEGER, PARAMETER :: end_unit_fortran = 300 162 163 ! Portio 164 INTEGER, PARAMETER :: start_unit_portio = 10 165 INTEGER, PARAMETER :: end_unit_portio = 300 166 167 ! NetCDF 168 INTEGER, PARAMETER :: start_unit_netcdf = 10 169 INTEGER, PARAMETER :: end_unit_netcdf = 300 ``` This suggests you can’t, by default, use the I/O server with netCDF outputs as both will want to use Unit number 10. I can’t see from the source code anyway to override these values via a namelist input. One fix is to set ```auto 168 INTEGER, PARAMETER :: start_unit_netcdf = 11 ``` or to set ```auto ! A flag which forces the portio list to use unique unit numbers 155 LOGICAL, PUBLIC :: portio_unique_units = .FALSE. ``` to `.TRUE.` (why would this be set to `.FALSE.` by default? 🤔 ), which suggests you have to recompile the code to use the I/O with netCDF outputs? I’m very surprised this is the case, but happy to proceed with this if required. What’s the best way to ask the UKMO about this? A Trac ticket? A post to [https://cms-helpdesk.ncas.ac.uk](https://cms-helpdesk.ncas.ac.uk) ? --- _[View the full topic](https://forum.access-hive.org.au/t/issues-with-configuring-the-um-i-o-server/4653)._