On Thu, Apr 05, 2001 at 04:25:42PM -0400, Ken Hirsch wrote:
> > > > TODO updated. I know we did number 2, but did we agree on #1 and is
> it
> > > > done?
> > >
> > > #2 is indeed done. #1 is not done, and possibly not agreed to ---
> > > I think Vadim had doubts about its usefulness, though personally I'd
> > > like to see it.
> >
> > That was my recollection too. This was the discussion about testing the
> > disk hardware. #1 removed.
>
> What is recommended in the bible (Gray and Reuter), especially for larger
> disk block sizes that may not be written atomically, is to have a word at
> the end of the that must match a word at the beginning of the block. It
> gets changed each time you write the block.
That only works if your blocks are atomic. Even SCSI disks reorder
sector writes, and they are free to write the first and last sectors
of an 8k-32k block, and not have written the intermediate blocks
before the power goes out. On IDE disks it is of course far worse.
(On many (most?) IDE drives, even when they have been told to report
write completion only after data is physically on the platter, they will
"forget" if they see activity that looks like benchmarking. Others just
ignore the command, and in any case they all default to unsafe mode.)
If the reason that a block CRC isn't on the TODO list is that Vadim
objects, maybe we should hear some reasons why he objects? Maybe
the objections could be dealt with, and everyone satisfied.
Nathan Myers
ncm@zembu.com