Re: Scatter-gather list constraints

[Jens Axboe]

On Thu, Jun 26 2008, Andi Kleen wrote:
> 
> > On the fs side, just setting a hw block size of 1k should fix the
> > problem, since that'd be your minimum transfer size AND alignment there
> > even for O_DIRECT IO.
> 
> XFS used to force 512 byte IOs for its log IO. Not sure
> that was ever fixed. If it was fixed it likely required a disk format
> change (I think s390 ran into a problem like this)

Issuing IO less than the hardware block size is illegal, so if they do
that then they can't be supported on hardware with > 512b block sizes.
Someone has to do the RMW for such an operation and we don't do it in
drivers.

-- 
Jens Axboe

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