mydumper much much slower than mysqldump - What am I doing wrong?

I am trying to backup a mysql database that is about 500 GB. mysqldump takes about 3-4 hours and the import is around 14 hours. Letting mydumper run on the DB for an hour now and it's only 1.1GB done. How is this faster? I have tried with 4 threads, 10 threads, 24 threads. The box has 24 cores and 64 GB of ram.

These are my command line options. Also, the db is on a NetApp AFF with 32 Gbps FC. Speed and IOPS are not the issue, we have checked.

#!/bin/sh DIR_BACKUP=/mysql_import DB_NAME=zabbix DB_USER=zabbix_user DB_PASS=1234 DOW=`date "+%a"` DB_DUMP=$DIR_BACKUP/dbdump.$DB_NAME.$DOW mydumper \ --database=$DB_NAME \ --host=$DB_HOST \ --user=$DB_USER \ --password=$DB_PASS \ --outputdir=$DB_DUMP \ --threads=24 \ --rows=5000000 \ --compress \ --build-empty-files \ --trx-consistency-only