On XO-1.5 with 11.3.0/11.3.1 -- hang during shutdown?

[John Gilmore]

I doubt that this issue is your problem.  But in response to one remark:

>                                  On the theory that these writes may
> be stalling due to the block number, (and we haven't seen any evidence
> yet of this), you can test for that by repeating the writes...

There *is* evidence that accesses to some block numbers in MLC flash
chips are much faster or slower than others (like 5x slower).  They
seem to be designed with "fast blocks" and "slow blocks", though this
is undocumented.  There is no interface for telling the software
which is which (except by actual measurement of the responsiveness of
the chip -- and in microSD cards, accesses are mediated by a Flash
Translation Layer of unknown characteristics).  See:

  Characterizing Flash Memory: Anomalies, Observations, and Applications
  Laura Grupp, Adrian Caulfield, Joel Coburn, Steven Swanson, Eitan Yaakobi and Paul Siegel
  UCSD Tech Report CS2009-0946
  August 19, 2009

Unfortunately the amazing people at UCSD fail to put up their archival
tech reports in readily accessible PDFs.  (It seems to be some sort of
half-assed DRM system, since they yammer about copyrights on the same
page.)  They do have a mangled (OCR'd!) abstract here:

  http://csetechrep.ucsd.edu/Dienst/UI/2.0/Describe/ncstrl.ucsd_cse/CS2009-0946

and a mangled 18MB PostScript version available here:

  http://csetechrep.ucsd.edu/Dienst/Repository/2.0/Body/ncstrl.ucsd_cse/CS2009-0946/postscript

The Wayback Machine failed to capture it while it was there.  But I
got the PDF from them when they had published it in 2009.  I have put
up the 1.5MB PDF temporarily here "for research purposes":

  http://www.toad.com/TEMP-Grupp-2009-TR-FTest.pdf

with the slides here:

  http://www.toad.com/TEMP-Grupp-2009-FMS-FTest.pdf
  
	John