Heb niks veranderd in die file maar dit is volgens mij wel wat we zochten:
# mdadm Debian configuration
#
# You can run 'dpkg-reconfigure mdadm' to modify the values in this file, if
# you want. You can also change the values here and changes will be preserved.
# Do note that only the values are preserved; the rest of the file is
# rewritten.
#
# INITRDSTART:
# list of arrays (or 'all') to start automatically when the initial ramdisk
# loads. This list *must* include the array holding your root filesystem. Use
# 'none' to prevent any array from being started from the initial ramdisk.
INITRDSTART='all'
# AUTOSTART:
# should mdadm start arrays listed in /etc/mdadm/mdadm.conf automatically
# during boot?
AUTOSTART=true
# AUTOCHECK:
# should mdadm run periodic redundancy checks over your arrays? See
# /etc/cron.d/mdadm.
AUTOCHECK=true
# START_DAEMON:
# should mdadm start the MD monitoring daemon during boot?
START_DAEMON=true
# DAEMON_OPTIONS:
# additional options to pass to the daemon.
DAEMON_OPTIONS="--syslog"
# VERBOSE:
# if this variable is set to true, mdadm will be a little more verbose e.g.
# when creating the initramfs.
VERBOSE=false
# MAIL_TO:
# this variable is now managed in /etc/mdadm/mdadm.conf (MAILADDR).
# Please see mdadm.conf(5).
Gisteren even wat zooi met een copy op me NAS gezet en zag dat er snel 2 retrans waren. Heb daarna de waarde van 8 naar 16 gezet. Daarna gemount met deze opties : rsize=32768,wsize=32768,intr,noatime
Haalde gelijk een write speed van 76MB/sec

is toch al zo'n 50% sneller. Ga nog wel wat verder tweaken vooral met de rsize en wsize die kan nog wat hoger.