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0 pointstecleandor3y ago0 comments

See my other comment but RAID 5/6 are not usually considered erasure coding implementations [0]. Mustly, because AFAIK RAID 5 and 6 aren't standards, so it depends on the controller or software manufacturer implementation. Some use XOR, some use Reed Solomon, some use other stuff...

For example, Linux MD RAID 5 uses XOR, and RAID 6 uses Galois fields. [1][2]

  0: https://www.itprotoday.com/storage/erasure-coding-vs-raid-which-right-and-when
  1: https://raid.wiki.kernel.org/index.php/A_guide_to_mdadm#Raid_5
  2: http://igoro.com/archive/how-raid-6-dual-parity-calculation-works/

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3 comments · 2 top-level

mjb3y ago· 1 in thread

Of course RAID 5 and 6 are erasure coding. They use a code (e.g. XOR/parity) to tolerate the behavior of a binary erasure channel (BEC). Systematic codes (where some of the code stripes are just identity chunks of the data), like RAID 5 and 6, are probably the most common case of erasure codes.

Now, we could have an argument about whether RAID 1 is an erasure code, but that wouldn't teach us much.

tecleandorOP3y ago

Well, I stand corrected (and I don't have much knowledge to argue about this).

Re-reading, I see that in the storage world "simple" correction systems don't tend to be classified as erasure coding.

Were I say "simple", I think I'd say any correction system that's not parametrizable, as in "let's do a 17+3 in this ordinary dataset and 4+2 in this one that's very important"

About RAID 1, technically probably it is... although bit very efficient :D

throwawaymaths3y ago

Technically xor is a special case of erasure coding.

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