死活打不开光驱dma

kd

如下:
[root@kd-server kd]# /sbin/hdparm -d1 /dev/hdc

/dev/hdc:
setting using_dma to 1 (on)
HDIO_SET_DMA failed: Operation not permitted
using_dma    =  0 (off)
硬盘可以顺利打开dma