Re: [PATCH v2 0/4] Support xxhash64 checksums

From: "Austin S. Hemmelgarn" <ahferroin7@gmail.com>
To: Adam Borowski <kilobyte@angband.pl>, Paul Jones <paul@pauljones.id.au>
Cc: "Peter Becker" <floyd.net@gmail.com>,
	"Holger Hoffstätte" <holger@applied-asynchrony.com>,
	"Linux BTRFS Mailinglist" <linux-btrfs@vger.kernel.org>
Subject: Re: [PATCH v2 0/4] Support xxhash64 checksums
Date: Mon, 26 Aug 2019 08:27:15 -0400	[thread overview]
Message-ID: <69ac4340-c782-aa92-246c-3106b1611eea@gmail.com> (raw)
In-Reply-To: <20190823170845.GD17075@angband.pl>

On 2019-08-23 13:08, Adam Borowski wrote:
> the improved collision
> resistance of xxhash64 is not a reason as if you intend to dedupe you want
> a crypto hash so you don't need to verify.

The improved collision resistance is a roughly 10 orders of magnitude 
reduction in the chance of a collision.  That may not matter for most, 
but it's a significant improvement for anybody operating at large enough 
scale that media errors are commonplace.

Also, you would still need to verify even if you're using whatever the 
fanciest new collision resistant cryptographic hash is, because the 
number of possible input values is still more than _nine thousand_ 
orders of magnitude larger than the total number of output values even 
if we use a 512-bit cryptographic hash.