XFS mount failuer on RAID5

[Christoph Hellwig]

On Mon, Oct 19, 2009 at 12:30:18PM +1100, Dave Chinner wrote:
> 
> IIRC, the main reason for 4k sectors on MD RAID5/6 is that changing
> the IO alignment from 4k to 512 byte IOs (i.e. sub-page sized)
> causes MD to flush and invalidate the stripe cache. Hence every
> time XFS writes a super block, AGF, AGFL or AGI, things go much
> slower because of this flush/invalidate. By setting the sector size
> to 4k, the SB/AGF/AGFL/AGI are all 4k in size and hence IO alignment

This should not happen anymore with 2.6 series kernels.