Changes between Version 111 and Version 112 of FAQ

Timestamp:

2015-08-24T17:54:15Z (9 years ago)

Author:

AzureCerulean

Comment:

--

FAQ

@@ -15 +15 @@
 '''[=#Q2_what_is_erasure_coding Q2:] "Erasure-coding"?  What's that?'''
 
-A: You know how with RAID-5 you can lose any one drive and still recover?  And there is also something called RAID-6 where you can lose any two drives and still recover.  Erasure coding is the generalization of this pattern: you get to configure how many drives you could lose and still recover.  You can choose how many drives (actually storage servers) will be used in total, from 1 to 256, and how many storage servers are required to recover all the data, from 1 to however many storage servers there are.  We call the number of total servers {{{N}}} and the number required {{{K}}}, and we write the parameters as "{{{K-of-N}}}".
-
-This uses an amount of space on each server equal to the total size of your data divided by {{{K}}}.
-
-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.
-
-"Forward error correction" is another term for erasure coding.
+A: RAID-5 can lose one drive and RAID-6 can lose two drives and recover. Using a method of data protection in which data is broken into fragments, expanded and codified with redundancies, stored across a selected set of various places or storage servers, Erasure coding (CE). The number of records (storage / servers / nodes) used in total can be chosen from 1 to 256, and the number of storage servers that are required to recover all the data, from 1 to the total number of available storage servers. The number of overall storage servers, we call {{{N}}} and the number needed {{{K}}} and write the parameters such that it is "{{{K-of-N}}}".
+
+This uses an amount of space on each storage server equal to the total size of your data is shared over all {{{K}}}.
+
+Tahoe-LAFS having default parameters {{{3-of-10}}}, the data is spread over 10 different disks and losing any 7, continue to recover all the data. This is more reliable than comparable RAID arrangements, with a cost of only 3.3 times the storage space that a single copy carries. 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.
+
+"Forward error correction" (FEC) 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 Algorithm" (IDA) can refer either to an erasure code or a secret sharing algorithm depending on context, so we prefer not to use that term.
+"Information Dispersal Algorithm" (IDA) can refer either to erasure code or secret sharing algorithm according to context, so we prefer not to use that term.
 
 '''[=#Q3_disable_encryption Q3:] Is there a way to disable the encryption for content which isn't secret? Won't that save a lot of CPU cycles?'''