I had similar problems with a MSI P45 board (ICH10) and mdadm raid6 
rebuild speed
bios default settings : 1 MB/s
enabling IDE busmaster: 22 MB/s
switching from IDE to AHCI: 33 Mb/s

Roelof


Ken Teh wrote:
> I solved the problem and thought I'd pass it along.  The BIOS also has 
> a SATA AHCI setting which was disabled.  After I enabled it, the disks 
> are now recognized as /dev/sd? and I'm getting more reasonable disk 
> speeds.  I also do not get the ata_piix message about "no available 
> legacy ports".
>
> Ken
>
> Ken Teh wrote:
>> I just installed SL5.3 on a Supermicro PDSBE motherboard and its disk 
>> i/o is painfully slow; about 3MB/s.  The system has SATA drives but 
>> the kernel sees them as /dev/hdx devices.  There is also a ata_piix 
>> message at the beginning of bootup that says "no available legacy 
>> port".  I'm guessing the failure to recognize the SATA drives as 
>> /dev/sdx and the slow disk i/o are related to this cryptic message.
>>
>> I ran a Fedora 11 live CD on the system and it can do disk i/o easily 
>> 20-30 times faster which is closer to what I expect.  100MB/s or 
>> more.  I'm pretty sure the problem is kernel related.
>>
>> I tried switching the SATA mode in the BIOS to compability instead of 
>> enhanced.  It didn't make any difference.  I wasn't expecting any.  
>> The compatibility vs native stuff, I thought, was something that was 
>> done when SATA support for spotty.  The SATA controller is an Intel 
>> ICH8 which I figure should be well supported.
>>
>> I also looked at the dumps of hdparm both under SL53 and Fedora 11.  
>> The features enabled are the same for both.  There are additional 
>> features listed under Fedora 11, all SCT (SMART Command Transport) 
>> related.  There is also a whole bunch of dma modes displayed in both 
>> hdparm -t dumps.  On SL53 there is a * next to udma5 while it's next 
>> to udma6 under Fedora.  I'm not sure what this means.
>>
>> Any ideas on how to proceed?  Build a custom kernel?  Which I am 
>> reluctant to do since I rely on SL for updates.
>>
>> Ken