lua-users home
lua-l archive

[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index] [Thread Index] 

Steve Heller wrote:


On Thu, 10 May 2007 02:02:04 -0400, Dave Dodge
<[email protected]> wrote:



This design requires that every unique block of data, in
every file in the filesystem, has a unique hash value.  A
collision results in data loss.

   "Using the Sha1 hash function, the probability of a
   collision is less than 10^-20. Such a scenario seems
   sufficiently unlikely that we ignore it [...]"

http://plan9.bell-labs.com/sys/doc/venti.html


For how big a filesystem? If you have enough blocks, the
probability of a collision will be 1.


Follow the link; the number quoted is for


[A] system that contains an exabyte (10^18 bytes) [a
million terabytes] stored as 8 Kbyte blocks (~10^14
blocks).


--
Aaron
http://arundelo.com/