ZFS dedup=skein (no verify)

rihad

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Hi. We have an atypical usage scenario that may benefit from using ZFS dedup (zdb -S reports 5x savings with compression+dedup, while compression alone is just 1.9x).
What are the implications of omitting verify with skein? Is silent data corruption possible? FreeBSD 11.2 / 12.0 amd64. Thanks.
 
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rihad

Active Member

Reaction score: 2
Messages: 109

Some food for thought coming from one of zfs coauthors.
When using a secure hash like SHA256, the probability of a hash collision is about 2^-256 = 10^-77 or, in more familiar notation, 0.00000000000000000000000000000000000000000000000000000000000000000000000000001. For reference, this is 50 orders of magnitude less likely than an undetected, uncorrected ECC memory error on the most reliable hardware you can buy.
http://automatica.com.au/2009/11/zfs-deduplication-jeff-bonwicks-blog/

How many bits does Skein algorithm use?
Does zfs somehow detect verify failures (i.e. hash collisions) and record them for viewing?
 
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