Re: Software RAID5 Horrible Write Speed On 3ware Controller!!

[Justin Piszcz <jpiszcz@lucidpixels.com>]

On Wed, 18 Jul 2007, Hannes Dorbath wrote:

> On 18.07.2007 13:19, Justin Piszcz wrote:
>> For the HW RAID tests (2) at the bottom of the e-mail, no, I did not set 
>> nr_requests or use the deadline scheduler.
>> 
>> For the SW RAID tests, I applied similar optimizations, I am probably not 
>> at the latest firmware.  The main thing I wanted to use though was SW RAID 
>> because the card itself offers so many ports, however, with write speed 
>> being that slow I am not sure its a good idea.
>
> I think what you might be experiencing is that XFS can read su,sw values from 
> the MD device and will automatically optimize itself, while it can't do that 
> for the HW RAID device. It is absolutely essential to align your file system, 
> to prevent implicit reads, needed for parity calculations.
>
> Set su to the stripe size you have configured in your controller (like 128K) 
> and sw to 9 (for a 10 disk RAID 5 array).
>
>
> -- 
> Regards,
> Hannes Dorbath
>

Yes I agree here, but I guess my question is why is SW RAID5 so slow on 
the 3ware card?

Justin.