[tahoe-dev] zfec right for me?

Markus Beyer m.beyer5 at gmx.de
Fri Jul 16 15:02:00 UTC 2010

Hi Jack,

thanks for your answer.

> > I am trying to build a data store for my files.
> > I would like to shield the file in it against corruption, eg bit errors
> on the disk and the like.
> > Can I achive this with zfec? If so, what m and k would you advice I use?
> I think (depending on your disk failure model) this could work well,
> though I don't have enough insight to offer particular suggestions on
> what parameters you would want.

Basicly, I want to use zfec to compensate for the shortcomings of a raid system. My storage is basicly a big raid partition that should prevent me from loosing Data due to disk failure, but as far as I can tell, it will never prevent any io errors, eg. bits that cannot be read back from the hard drive. I am looking for a sollution to compensate for those things.
Any recomondations on your part are welcome though :)

> > Also, does zfec have the ability to detect if one of the pieces is
> > corrupted so it won't be used for reconstruction of the original
> > (leading to corrupt original data) ?
> No it does not - you'll want to use an external checksum for this
> purpose.

How would you recommend I store this?
I think I would need a redundant checksum, but in case one is altered / messed up, how do I guarantee the correct one is picked for varification?

> (A while back I put together a draft of a new file format for zfec
> that will be more useful in the general case, for instance with easily
> identifiable magic numbers, per-share checksums, etc - right now zfec
> only implements the bare error correction code. However I haven't had
> time to flesh it out and actually implement it, so for the time being
> with zfec you're more or less on your own with the error checking and
> so forth).

That would be nice. If you plan to get back to it some time in the future, I would love to have a look at your spect and maybe offer some feedback.

Best regards,
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