Tips and tricks: Why am I not able to activate DMA mode for my IDE HDD/CD on ICH7 chipset?

Contributed by Anders Karlsson

Release Found: Red Hat Enterprise Linux 5

In a system with a ICH7 chipset and a IDE HDD and/or a CD/DVD attached to the system, very slow I/O performance may be observed under Red Hat Enterprise Linux 5. The reason for the potential problem is that when two drivers share hardware, one loses DMA capability. If the hardware and BIOS permits, one can switch from combined or legacy mode to native, AHCI or RAID mode.

To verify HDD performance, run the following command:

# hdparm -t /dev/hda

For the cases where the BIOS does not allow switching to native, AHCI or RAID mode, append

combined_mode=libata

or

combined_mode=ide

to the kernel command line options, as this will work around the problem. Best option is to boot the system, interrupt grub and edit the entries to add the above line on a temporary basis while testing it. If satisfied with the results from testing, edit /boot/grub/grub.conf and add the option in permanently.

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This entry was posted by the editorial team on Monday, October 22nd, 2007 at 8:07 am and is filed under tips and tricks, technical. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.