Home » LPI » 117-201 » What command must be run to enable DMA on it?
One of the IDE hard drives in a server is transferring data very slowly. What command must be run to enable DMA on it?
A. hdparm -d /dev/hda
B. hdparm –dma /dev/hda
C. hdparm –dma /dev/hda1
D. hdparm -d /dev/hda1
E. hdparm -d 1 /dev/hda
Correct Answer: E
Explanation/Reference:
Explanation:
hdparm provides a command line interface to various hard disk ioctls supported by the stock Linux ATA/IDE device driver subsystem. Some options may work correctly only with the latest kernels.
-d Disable/enable the "using_dma" flag for this drive. This option now works with most combinations of drives and PCI interfaces which support DMA and which are known to the IDE driver. It is also a good idea to use the appropriate -X option in combination with -d1 to ensure that the drive itself is programmed for the correct DMA mode, although most BIOSs should do this for you at boot time. Using DMA nearly always gives the best performance, with fast I/O throughput and low CPU usage. But there are at least a few configurations of chipsets and drives for which DMA does not make much of a difference, or may even slow things down (on really messed up hardware!). Your mileage may vary.
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