Re: [gentoo-user] linux' IO performance sucks

[Daniel <danny@ilievnet.com>]

Sven Köhler wrote:
> Hi,
> 
> sorry for the silly subject, but did you ever experience the following?:
> 
> i have a fileserver, i copy a file to it - let's say 600MB.
> 
> So about every 200MB (i guess the linux box writes the data into the
> cache in the RAM first) linux writes the harddisk. But during that time
> - during the time it writes that 200MB to disk, there is no chance for
> any other IO. I'm playing an mp3 from the very same fileserver. It stops
> playing, because the machine does answer the read-requests.
> 
> So what's going on here?
> 
> Why does Linux write so huge amounts of data to the disk? Why does Linux
> not stop writing for a while to fullfil the read-requests? And so on ...
> 
> Any idea, on how to imrpove that?
> 

Perhaps a more often flush of buffers may help you in this situation.

There are several parameters you can tweak to control your kernel
behavior regarding this.

You can put the following lines in your /etc/sysctl.conf file, replacing
 "i","j","k" and "l" with proper numbers.
vm.dirty_expire_centisecs =  i
vm.dirty_writeback_centisecs = j
vm.dirty_ratio = k
vm.dirty_background_ratio = l

The meaning of these parameters is descibed in the kernel documentation:
/usr/src/linux/Documentation/filesystems/proc.txt
/usr/src/linux/Documentation/sysctl/vm.txt

You could also disable all write caching by issuing the command:

hdparm -W0 /dev/<your-physical-disk-name>


Hope This Helps

---
Best regards
Daniel
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