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List:       linux-btrfs
Subject:    Re: RAID1C3 across 3 devices but with only 2 online simultaneously
From:       Chris Murphy <lists () colorremedies ! com>
Date:       2020-04-29 1:11:22
Message-ID: CAJCQCtQjEgYmEs28usUe-sh_KpX9jsFgDUT=xkGNf1FkH-tKBQ () mail ! gmail ! com
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On Tue, Apr 28, 2020 at 6:25 PM Zygo Blaxell
<ce3g8jdj@umail.furryterror.org> wrote:

> Doing this with scrub is not reliable with the crc32c csum method--every
> ~16TB of updates, you'll get a crc32c collision, so you'll have the
> wrong data on disk and no csum failure to detect it with.  Any of the
> other csum options will solve this.  Use SHA256 if (and only if) you
> are worried about crypto collision attacks in your data; otherwise,
> xxhash64 is fine.

What about blake2b? Hash benchmark on x86_64 shows it's quite a lot
faster than SHA256 (and yet still way slower than xxhash64 or crc32c).
But I have no idea if this actually affects overall file system
read/write performance when under load.

I've started to migrate to xxhash64. It'd be nice to have a convert
option. Rewriting 100% of the metadata is still a fraction of having
to rewrite out TBs of data. But this is not a complaint. Btrfs is
still badass.

-- 
Chris Murphy
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