sbp2 scatter/gather - near future trouble

Pat LaVarre lavarre at
Wed Jul 4 06:54:36 PDT 2001

* From the T10 Reflector (t10 at, posted by:
* "Pat LaVarre" <lavarre at>
My mail client tells me it quietly truncated my mail titled "sbp2 
scatter/gather - "great loss" of speed".  Continuing therefore where I left 
off ...

 > <ewa at> 07/04/01 01:00 AM
 > t10 at

I'm also aware of people who think everything on a 16-bit ATA bus involves 
pairs of bytes.  Intensely influential people, like the author of Microsoft's 
Win95B Esdi506.pdr Atapi.  The world is too full of normal people.  Soon 
enough, we're going to find people building stuff that chokes unless aligned 
to 64 bit boundaries.

What's the process we have in place to keep the newbie customer from buying 
and shipping excessively cheap silicon?  How do we stop this problem from 

 > Apple ... painfully double-buffer some I/O ...

I hear the Apple FireWire mass storage driver double-buffers as needed to 
align data to x10 byte boundaries?

This is an interesting choice.  x10 is often the size of a cache line on the 
motherboard.  As we've been discussing, we know we see trouble if for all 
devices we guarantee no alignment.  I wonder if we'll see trouble if for all 
devices we guarantee no more than 4 byte alignment?

Thanks again in advance.    Pat LaVarre <p.lavarre at> 

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