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Re: Using free space for more fault tolerant file systems.

Cross-posted to 5 groups.

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John Gordon wrote:
> In <86sjnhbtht.fsf@zipcon.net> Patrick Scheible <kkt@zipcon.net> writes:
> 
>> What you describe would save you in the event of a bad sector
> 
> It would only save you if there's enough free space to clone the
> entire drive, or if the bad sector happened to be chosen for duplication
> in the remaining free space.
> 

I bet you could make use of the space.

Think "QuickPar". (This article doesn't do it justice, but you have to
start somewhere.)

http://en.wikipedia.org/wiki/Quickpar

QuickPar was proposed as a "belt and suspenders" method of storing
data on CDs. For example, you'd write 500MB worth of files, and
store an additional 200MB of parity blocks. If you took a nail, and scratched
200MB of data on the CD, the remaining parity blocks could be used to
re-constitute the original data.

The PAR method is typically used on USENET, in binary groups, for pirating
movies. A movie might be chopped up into a thousand USENET postings to a
binary group. USENET servers may have poor retention, or lose some of the
postings. If the user then injects a significant percentage of parity blocks,
recipients on the other end, downloading the movie, could download the available
eight hundred data blocks, two hundred or more parity blocks, and get the entire
movie to show up on their desktop (as the parity blocks can be used to
replace the missing data). So the concept was popularized in pirating
circles, and most of the testing would be done there (as to what works and
what doesn't work).

One of the problems with PAR, was the implementation was less than perfect.
There is a "maths" problem with the tools in popular circulation, such that
you can't always recover the data. There were some proposals on how to fix
that (some kind of sparse matrix of some sort), but I stopped following
the conversation on the subject. I did some testing, i.e. remove a block
of data, grab a parity block, and see the tool recover the data, so it
did work in very limited testing. But there are reports, from people
who have enough parity blocks but can't get the data back.

    Paul

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Using free space for more fault tolerant file systems. "Skybuck Flying" <Windows7IsOK@DreamPC2006.com> - 2011-09-27 19:03 +0200
  Re: Using free space for more fault tolerant file systems. "Skybuck Flying" <Windows7IsOK@DreamPC2006.com> - 2011-09-27 19:06 +0200
  Re: Using free space for more fault tolerant file systems. Patrick Scheible <kkt@zipcon.net> - 2011-09-27 13:49 -0700
    Re: Using free space for more fault tolerant file systems. John Gordon <gordon@panix.com> - 2011-09-27 21:21 +0000
      Re: Using free space for more fault tolerant file systems. Paul <nospam@needed.com> - 2011-09-27 18:05 -0400
        Re: Using free space for more fault tolerant file systems. Nobody <nobody@nowhere.com> - 2011-09-28 02:13 +0100
    Re: Using free space for more fault tolerant file systems. "Skybuck Flying" <Windows7IsOK@DreamPC2006.com> - 2011-09-28 11:47 +0200
  Re: Using free space for more fault tolerant file systems. China Blue Corn Chips <chine.bleu@yahoo.com> - 2011-09-28 06:26 -0700
    Re: Using free space for more fault tolerant file systems. "Skybuck Flying" <Windows7IsOK@DreamPC2006.com> - 2011-09-28 16:39 +0200
      Re: Using free space for more fault tolerant file systems. "Skybuck Flying" <Windows7IsOK@DreamPC2006.com> - 2011-09-28 16:43 +0200

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