CDO

I use the data from ftp://podaac-ftp.jpl.nasa.gov/allData/merged_alt/L4/cdr_grid

Here is the metadata of one of the files:

netcdf ssh_grids_v1609_2014122612 {
  dimensions:
    Latitude = 960 ;
    Longitude = 2160 ;
    Time = UNLIMITED ; // (1 currently)
    nv = 2 ;

  variables:
    float Lat_bounds(Latitude,nv) ;
      Lat_bounds:units = "degrees_north" ;
      Lat_bounds:comment = "latitude values at the north and south bounds of each pixel." ;

    float Latitude(Latitude) ;
      Latitude:bounds = "Lat_bounds" ;
      Latitude:point_spacing = "even" ;
      Latitude:long_name = "latitude" ;
      Latitude:standard_name = "latitude" ;
      Latitude:units = "degrees_north" ;
      Latitude:axis = "Y" ;

    float Lon_bounds(Longitude,nv) ;
      Lon_bounds:units = "degrees_east" ;
      Lon_bounds:comment = "longitude values at the west and east bounds of each pixel." ;

    float Longitude(Longitude) ;
      Longitude:bounds = "Lon_bounds" ;
      Longitude:point_spacing = "even" ;
      Longitude:long_name = "longitude" ;
      Longitude:standard_name = "longitude" ;
      Longitude:units = "degrees_east" ;
      Longitude:axis = "X" ;

    float SLA(Time,Longitude,Latitude) ;
      SLA:_FillValue = 9.96921e+36f ;
      SLA:scale_factor = 1.f ;
      SLA:coordinates = "Sea Level Anomaly Estimate" ;
      SLA:add_offset = 0.f ;
      SLA:long_name = "Sea Level Anomaly Estimate" ;
      SLA:standard_name = "Sea Level Anomaly Estimate" ;
      SLA:units = "m" ;

    float SLA_ERR(Time,Longitude,Latitude) ;
      SLA_ERR:_FillValue = 9.96921e+36f ;
      SLA_ERR:scale_factor = 1.f ;
      SLA_ERR:coordinates = "Sea Level Anomaly Error Estimate" ;
      SLA_ERR:add_offset = 0.f ;
      SLA_ERR:long_name = "Sea Level Anomaly Error Estimate" ;
      SLA_ERR:standard_name = "Sea Level Anomaly Error Estimate" ;
      SLA_ERR:units = "m" ;

    float Time(Time) ;
      Time:bounds = "Time_bounds" ;
      Time:long_name = "Time" ;
      Time:standard_name = "time" ;
      Time:units = "Days since 1985-01-01 00:00:00" ;
      Time:calendar = "gregorian" ;
      Time:axis = "T" ;

    float Time_bounds(Time,nv) ;
      Time_bounds:units = "Days since 1985-01-01 00:00:00" ;
      Time_bounds:comment = "Time bounds for each time value, same value as time variable. The time variable is defined on points instead of on bounding boxes." ;

  // global attributes:
    :geospatial_lon_min = 0.08333334f ;
    :geospatial_lat_max = 79.91666f ;
    :time_coverage_end = "2014-12-26" ;
    :title = "Sea Level Anormaly Estimate based on Altimeter Data" ;
    :geospatial_lat_min = -79.91666f ;
    :time_coverage_start = "2014-12-26" ;
    :Conventions = "CF-1.6" ;
    :date_created = "2016-09-11T18:07:15.140757" ;
    :summary = "Sea level anomaly grids from altimeter data using Kriging technique, which gives best linear prediction based upon prior knowledge of covariance. " ;
    :ncei_template_version = "NCEI_NetCDF_Grid_Template_v2.0" ;
    :Institution = "Jet Propulsion Laboratory" ;
    :geospatial_lon_max = 359.9167f ;
    :version_number = "1609" ;

} // group /

My CDO version is below

cdo -V
Climate Data Operators version 1.7.2 (http://mpimet.mpg.de/cdo)
Compiled: by scidb on scidb-vm (x86_64-unknown-linux-gnu) Sep 19 2016 13:48:25
Compiler: gcc -std=gnu99 -g -O2 -fopenmp
 version: gcc (Ubuntu 4.8.5-2ubuntu1~14.04.1) 4.8.5
Features: DATA PTHREADS OpenMP3 HDF5 NC4/HDF5/threadsafe OPeNDAP PROJ.4 SSE2
Libraries: HDF5/1.8.15 proj/4.8
Filetypes: srv ext ieg grb grb2 nc nc2 nc4 nc4c
     CDI library version : 1.7.2 of Sep 19 2016 13:46:56
 CGRIBEX library version : 1.7.5 of Jun  3 2016 14:44:00
GRIB_API library version : 1.13.1
  NetCDF library version : 4.3.3.1 of Sep 19 2016 13:23:52 $
    HDF5 library version : 1.8.15 threadsafe
 SERVICE library version : 1.4.0 of Sep 19 2016 13:46:34
   EXTRA library version : 1.4.0 of Sep 19 2016 13:46:26
     IEG library version : 1.4.0 of Sep 19 2016 13:46:31
    FILE library version : 1.8.2 of Sep 19 2016 13:46:26

I try to perform nearest-neighbor interpolation like this (increase the resolution twice, 2x):

 time cdo remapnn,r4320x1920 ssh_grids_v1609_2014122612.nc o.nc
Warning (cdfScanVarAttributes) : NetCDF: Variable not found - Sea
Warning (cdfScanVarAttributes) : NetCDF: Variable not found - Level
Warning (cdfScanVarAttributes) : NetCDF: Variable not found - Anomaly
Warning (cdfScanVarAttributes) : NetCDF: Variable not found - Error
Warning (cdfScanVarAttributes) : NetCDF: Variable not found - Estimate
cdo remapnn: Nearest neighbor weights from lonlat (2160x960) to lonlat (4320x1920) grid, with source mask (1411453)

Error (gridDefBoundsGeneric) : Allocation of 265420800 bytes failed. [ line 3136 file grid.c ]
System error message : Cannot allocate memory

real    5m6.203s
user    5m2.712s
sys     0m1.492s

• It takes too long for remapnn to complete. Nearest-neighbor is not a time-intensive operation, why does it take this time? To compare: when I convert this file to GeoTIFF and do the same with gdalwarp it takes just several seconds vs 5 minutes...
• Memory allocation failure.

What I am doing wrong? Is there a way to speed up the processing?

Thanks