expdp takes more than ten times longer to run

Hello,

We are running Oracle Database 12.1.0.1.0 on Centos 6.6.

We are running this command to make the expdp:

expdp ops$querix/password  \

SCHEMAS=OPS$QUERIX\

LOGTIME=ALL METRICS=YES \

DIRECTORY=DUSA_DATA_PUMP_DIR \

FILESIZE=2GB REUSE_DUMPFILES=YES \

DUMPFILE=DU_EXP_SCHEMAS_%U \

LOGFILE=DU_EXP_SCHEMAS_PRUEBA.log \

JOB_NAME=DU_EXP_SCHEMAS_PRUEBA

The problem is that this command, from one day to another, is taking 36 hours, while it usually took 30 minutes.

What I did to try to solve the issue:

-We have statistics updated statistics with:

     EXEC dbms_stats.gather_database_stats;

-Also, I don't think there's an IO bottleneck, since while backing up, system load is low, and 'vmstat 1' shows no IO wait.