From: Evan Felix <evan.felix@pnl.gov>

Here is a patch that fixes a major issue in the raid5/6 code.  It seems
that the code:

logical_sector = bi->bi_sector & ~(STRIPE_SECTORS-1);
(sector_t)     = (sector_t)    & (constant)

that the right side of the & does not get extended correctly when the
constant is promoted to the sector_t type.  I have CONFIG_LBD turned on so
sector_t should be 64bits wide.  This fails to properly mask the value of
4294967296 (2TB/512) to 4294967296.  in my case it was coming out 0.  this
cause the loop following this code to read from 0 to 4294967296 blocks so
it could write one character.

As you might imagine this makes a format of a 3.5TB filesystem take a very
long time.