Re: [boost] Random Access to Files (RAF) - any interest ?

From: Tomas Puverle (Tomas.Puverle_at_[hidden])
Date: 2006-05-23 18:09:49

> Totally agree about more general solution.
> 
> That does not change anything, but just out of curiosity some
> calculations were made: the number of atoms in the graphite of a
> pencil is < 2^72,
> 
> http://www.madsci.org/posts/archives/oct98/905633072.As.r.html
> 
> so the storage providing capacity to hold files with 128-bit offset
> would have to contain at least as many atoms as 8*2^56 = 2^59 pencil
> leads ! Hundreds of tons of material that should be. And this is with
> just 1 atom per bit of information. Seems a bit too much for any
> conceivable technology... What FS would need to provide support for
> such capacities ?

Agreed, it would be a lot of data.  However, I was mistaken about the maximum 
file size.  It seems that even on the very large filesystems such as ZFS and 
the Veritas VxFS, the maximum size of an individual file is only 2^64.

Look here:

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

under the section "Limits". 

With regards to your calculation,  Jeff Bonwick, the designer of ZFS 
filesystem made a similar calculation to yours in one of his initial blog 
posts:

"Although we'd all like Moore's Law to continue forever, quantum mechanics 
imposes some fundamental limits on the computation rate and information 
capacity of any physical device. In particular, it has been shown that 1 
kilogram of matter confined to 1 liter of space can perform at most 1051 
operations per second on at most 1031 bits of information [see Seth 
Lloyd, "Ultimate physical limits to computation." Nature 406, 1047-1054 
(2000)]. A fully-populated 128-bit storage pool would contain 2128 blocks = 
2137 bytes = 2140 bits; therefore the minimum mass required to hold the bits 
would be (2140 bits) / (1031 bits/kg) = 136 billion kg.

To operate at the 1031 bits/kg limit, however, the entire mass of the computer 
must be in the form of pure energy. By E=mc2, the rest energy of 136 billion 
kg is 1.2x1028 J. The mass of the oceans is about 1.4x1021 kg. It takes about 
4,000 J to raise the temperature of 1 kg of water by 1 degree Celcius, and 
thus about 400,000 J to heat 1 kg of water from freezing to boiling. The 
latent heat of vaporization adds another 2 million J/kg. Thus the energy 
required to boil the oceans is about 2.4x106 J/kg * 1.4x1021 kg = 3.4x1027 J. 
Thus, fully populating a 128-bit storage pool would, literally, require more 
energy than boiling the oceans."