[T10] SBP 1394 hard drives hang with Windows XP (rare)

Eric Anderson ewa at apple.com
Tue May 6 10:50:47 PDT 2003

Hi everyone,

Like Peter said, we expect drives to comply with the SBP and 1394
specifications.  However, SBP-2 had some wording that, with effort, could
be misunderstood as to suggest that quadlet alignment was guaranteed -
which is not true.  We've cleared up the wording in SBP-3, but some earlier
1394-ATA silicon does have trouble with unaligned access (whether or not it
exceeds ~255 blocks).

No formal standard exists to identify this flaw in drives, but some OS
providers are able to tolerate the problem.  The key word here is
"tolerate"; usually workarounds cause reduced performance and are not a
replacement for complying with the standards.

If you find that a drive is failing on a particular OS, I recommend that
you contact the OS and drive vendors for a resolution.  If you are entering
the 1394 drive market, I suggest that you require your silicon vendor to
fully comply with 1394 and SBP, and to certify that they do not have this


>* From the T10 Reflector (t10 at t10.org), posted by:
>* Peter Johansson <PJohansson at ACM.org>
>At 09:58 AM 5/2/2003 -0600, Pat LaVarre wrote:
>>I have heard rumours of a coordinated Apple/ Microsoft effort to let a 
>>1394 device declare that it works best with a four-byte-aligned physical 
>>address, but I don't know anything more specific than that.
>No proposal remotely similar to this rumor was brought forward by either 
>Apple or Microsoft during the development of SBP-3. If there was credible 
>interest in this idea, the SBP-3 working group would have been the place
>discuss it.
>It's not a particularly good idea. What does "works best" translate to? 
>Doesn't work at all with other alignments? This simply adds complexity to 
>initiator implementations for little practical value. Because an SBP-3 
>target uses Serial Bus block read and block write requests to transfer
>and because these requests, by definition, accept arbitrary byte
>and lengths, it is not an undue requirement to expect SBP-3 targets to 
>operate correctly with arbitrarily aligned buffers.
>Peter Johansson
>Congruent Software, Inc.
>98 Colorado Avenue
>Berkeley, CA  94707
>(510) 527-3926
>(510) 527-3856 FAX
>PJohansson at ACM.org

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