# What is hdparm "readahead"?

## net_keeper

Hy,

Before some time I have complaint that my gentoo is slower than my old mandrake.

Well,

It have been fix with hdparm.

Now I have reset to my old mandrake and I found a different in the hdparm output.

Mandrake hdparm output:

/dev/hda:

 multcount    = 16 (on)

 IO_support   =  1 (32-bit)

 unmaskirq    =  1 (on)

 using_dma    =  1 (on)

 keepsettings =  0 (off)

 readonly     =  0 (off)

 readahead    =  8 (on)

 geometry     = 4865/255/63, sectors = 78165360, start = 0

And in my gentoo:

/dev/hda:

 multcount    = 16 (on)

 IO_support   =  1 (32-bit)

 unmaskirq    =  1 (on)

 using_dma    =  1 (on)

 keepsettings =  0 (off)

 readonly     =  0 (off)

 readahead    = 256 (on)

 geometry     = 12009/16/63, sectors = 78165360, start = 0

Is the different is affective? Which is faster?

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## pilla

Have you read "man hdparm" ? The meaning of the read-ahead flag is described there.

You need to know what you want to maximize in your system (throughput x response) and run some benchmarking before you decide which one is better for you.

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## TobiWan

Hi there,

while we're at it I thought I could just drop a question related to DMA and harddisks. While booting, I get a message in a nice ascii box, that devfs might be slowed down due to turned off dma. I can enable it using hdparm but the next time I boot, the message stays. Where can I set the dma permamently?

thanks in advance for a probably stupid question,

Tobias

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## hensan

Put your settings in /etc/conf.d/hdparm

Then do: rc-update add hdparm default

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## TobiWan

many thanks, that does the trick!

this should go into http://www.gentoo.org/doc/en/gentoo-x86-install.xml  :Wink: 

cheers,

Tobias

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