RE: Very slow disk performance on CentOS 4.5

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From: centos-bounces@xxxxxxxxxx 
[mailto:centos-bounces@xxxxxxxxxx] On Behalf Of Bart Schaefer
> 
> On 8/31/07, Alfred von Campe <alfred@xxxxxxxxxxxxx> wrote:
> > The are all SATA drives (2 HDDs and 2 optical drives).  But because
> > there are two controllers, one of the HDDs shows up as /dev/hda and
> > the other as /dev/sda.
> 
> If it's showing up as /dev/hda, it's probably being accessed in legacy
> IDE compatibility mode or some such thing.  Check your BIOS.
> 
> (With CentOS 3, any time I upgrade the kernel, I have to switch my
> SATA drives into legacy mode before lilo will write the boot sector
> properly, and then switch them back again when rebooting.)

Yes, I was going to say this too, make sure the SATA settings in the
BIOS are all set to SATA operation and not "legacy", then you should
see /dev/sda and /dev/sdb and all DMA, IO size, NCQ and multiple sector
settings will be properly negotiated at start-up.

To set these via hdarpm:

hdparm -c 1 /dev/hda (for 32-bit)
hdparm -d 1 /dev/hda (for DMA)
hdparm -m 16 /dev/hda (multiple sector IO = 16 sectors)

These can be combined to: hdparm -c 1 -d 1 -m 16 /dev/hda

-Ross

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