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describe the difference between erasure coding and secret sharing 

[Imported from Trac: page FAQ, version 97]
daira 2013-07-29 10:28:31 +00:00
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FAQ.md

@ -20,7 +20,11 @@ This uses an amount of space on each server equal to the total size of your data
The default Tahoe-LAFS parameters are `3-of-10`, so the data is spread over 10 different drives, and you can lose any 7 of them and still recover the entire data. This gives much better reliability than comparable RAID setups, at a cost of only 3.3 times the storage space that a single copy takes. It takes about 3.3 times the storage space, because it uses space on each server equal to 1/3 of the size of the data, and there are 10 servers. The default Tahoe-LAFS parameters are `3-of-10`, so the data is spread over 10 different drives, and you can lose any 7 of them and still recover the entire data. This gives much better reliability than comparable RAID setups, at a cost of only 3.3 times the storage space that a single copy takes. It takes about 3.3 times the storage space, because it uses space on each server equal to 1/3 of the size of the data, and there are 10 servers.
Erasure coding is also known as "forward error correction". "Forward error correction" is another term for erasure coding.
Erasure coding should not be confused with "secret sharing", which has the additional security property that fewer than `K` servers cannot recover any information about the data. Tahoe-LAFS' erasure coding does not have this property, and does not need to have it because we rely on secret-key encryption (using a key in the read cap) for confidentiality.
"Information Dispersal Code" (IDA) can refer either to an erasure code or a secret sharing algorithm depending on context, so we prefer not to use that term.
**<a name="Q3_disable_encryption">Q3:</a> Is there a way to disable the encryption for content which isn't secret? Won't that save a lot of CPU cycles?** **<a name="Q3_disable_encryption">Q3:</a> Is there a way to disable the encryption for content which isn't secret? Won't that save a lot of CPU cycles?**