Calculating swidth On A RAID6 Volume

[Michael Weissenbacher]

Michael,
>> If that is the case, then here is what I would expect my values to
>>  be: sunit = 512
>> swidth = 4608
>  
> I think sunit should be as big as the RAID controllers stripe size, as 
> it describes the smallest I/O XFS should do. So sunit=512 would make it 
> possible that XFS writes a single sector, while the RAID controller 
> needs to read/write 256KB with your stripe size, resulting in 
> performance degradation. But I'm no XFS dev, so maybe wait for a 
> clearing from someone who has deeper XFS knowledge than me.
> 
> sunit=262144
> swidth=9
> 
> Would be my suggestion for your setup.
> 
IIRC sunit and swidth are both specified in units of 512 bytes (don't
ask me why) so a sunit value of 512 would mean 256KB stripe size which
is correct :-)

If i am right, the FAQ should be corrected (hopefully some dev can
confirm/deny it)

cheers,
Michael