Using XDBC I tried to retrieve and/or update data of a COBOL file and get, when the COBOL file is bigger than 4 gigabytes, this error on the SELECT statement:
 
17:21:19,995 ERROR [Application] ...
scan, sqlState = 07000
java.sql.SQLException: executeQuery exception: MFEXTFH: Cannot open 'FileNAme',No space in directory or directory does not exist
 at vortex.sql.vortexPreparedStatement.executeQuery(vortexPreparedStatement.java:154)
 at org.jboss.resource.adapter.jdbc.CachedPreparedStatement.executeQuery(CachedPreparedStatement.java:90)

You have to set the File Handler option FILEMAXSIZE=8 in an File Handler configuration file
and for convenience set an EXTFH environment variable pointing to the full pathname of the File Handler configuration file.

(This is documented in Net Express like Server Express documentation)
(File Handling->Chapter 6: File Handler Configuration)

Content of File Handler configuration file: 
[XFH-DEFAULT]
FILEMAXSIZE=8

-> sample script to set EXTFH environment environment variable and set FILEMAXSIZE=8 in File Handler configuration file:
EXTFH=/home/MFFH.cfg
export EXTFH
echo [XFH-DEFAULT] >$EXTFH
echo FILEMAXSIZE=8 >>$EXTFH

Depending on the XDBC configuration you are using
  IF Stand-Alone Configuration:  EXTFH & File Handler configuration file   have to be set before to launch the XDBC application
  IF Network Configuration:        EXTFH & File Handler configuration file   have to be set before to launch the the XDBC server