Re: [RFC PATCH] Btrfs: add sha256 checksum option

[Austin S Hemmelgarn <ahferroin7@gmail.com>]

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On 2014-11-26 08:38, Brendan Hide wrote:
> On 2014/11/25 18:47, David Sterba wrote:
>> We could provide an interface for external applications that would make
>> use of the strong checksums. Eg. external dedup, integrity db. The
>> benefit here is that the checksum is always up to date, so there's no
>> need to compute the checksums again. At the obvious cost.
>
> I can imagine some use-cases where you might even want more than one
> algorithm to be used and stored. Not sure if that makes me a madman,
> though. ;)
>
Not crazy at all, I would love to have the ability to store multiple 
different weak but fast hash values.  For example, on my laptop, it is 
actually faster to compute crc32c, adler32, and md5 hashes together than 
it is to compute pretty much any 256-bit hash I've tried.

This then brings up the issue of what to do when we try to mount such a 
fs on a system that doesn't support some or all of the hashes used.


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