Changes between Version 16 and Version 17 of FAQ


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Timestamp:
2010-03-08T08:08:12Z (15 years ago)
Author:
zooko
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edit

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  • FAQ

    v16 v17  
    77Q: "Erasure-coding"?  What's that?
    88
    9 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 it for how many drives you could lose and still recover.  Tahoe-LAFS is typically configured to upload each file to 10 different drives, where you can lose any 7 of them and still recover the entire file.  This gives radically better reliability than typical RAID setups, at a cost of only 3.3 times the storage space that a single copy takes.
     9A: 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 it for how many drives you could lose and still recover.  Tahoe-LAFS is typically configured to upload each file to 10 different drives, where you can lose any 7 of them and still recover the entire file.  This gives radically better reliability than typical RAID setups, at a cost of only 3.3 times the storage space that a single copy takes. (This technique is also known as "forward error correction" and as an "information dispersal algorithm".)
    1010
    1111Q: Is there a way to disable the encryption phase and just use the encoding on the actual content? Won't that save a lot of CPU cycles?