Tu as dû manqué le coche vers la fin du script /etc/rc.d/rc.sysinit.
Extrait:
# Turn on harddisk optimization
# There is only one file /etc/sysconfig/harddisks for all disks
# after installing the hdparm-RPM. If you need different hdparm parameters
# for each of your disks, copy /etc/sysconfig/harddisks to
# /etc/sysconfig/harddiskhda (hdb, hdc...) and modify it.
# Each disk which has no special parameters will use the defaults.
# Each non-disk which has no special parameters will be ignored.
#