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Date:      Mon, 9 Nov 2015 20:55:11 +0000
From:      Steven Hartland <steven@multiplay.co.uk>
To:        Tim Gustafson <tjg@ucsc.edu>
Cc:        "freebsd-fs@freebsd.org" <freebsd-fs@freebsd.org>
Subject:   Re: ZFS RAID 0+1 Throwing Checksum Errors
Message-ID:  <-7786625913476013857@unknownmsgid>
In-Reply-To: <CAPyBAS7oYvp6vvzetcGmrXy0_Qn0fXBN_d510w41CguDZCzMxw@mail.gmail.com>
References:  <CAPyBAS7oYvp6vvzetcGmrXy0_Qn0fXBN_d510w41CguDZCzMxw@mail.gmail.com>

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I would check for bad memory or cabling. If you have a hot swap
midplane  and the disks are linked at 6gbps that could also be the
issue. In short it's more likely to be a hardware issue than software

> On 9 Nov 2015, at 19:09, Tim Gustafson <tjg@ucsc.edu> wrote:
>
> I have a FreeBSD 10.1 server configured as root-on-zfs with the
> following pool configuration:
>
> NAME            STATE     READ WRITE CKSUM
> tank           ONLINE       0     0     0
> mirror-0      ONLINE       0     0     0
>   gpt/zfs0    ONLINE       0     0     0
>   gpt/zfs1    ONLINE       0     0     0
> mirror-1      ONLINE       0     0     0
>   gpt/zfs2    ONLINE       0     0     0
>   gpt/zfs3    ONLINE       0     0     0
>
> The disks are each 1TB Samsung 850EVO SSDs connected via an mrsas Dell
> Perc raid controller configured in "RAID Disabled" mode.
>
> I run a "zpool scrub" every weekend and every weekend the scrub finds
> a handful (usually between 1 and 10) checksum errors per disk.  The
> scrub fixes the checksum errors, and I clear the counters and
> everything seems fine.  As far as I know, I do not have any corrupt or
> missing data.
>
> The server is a fairly busy web and database server, handling about 5
> million hits per day.
>
> I'm wondering if the problem is that the scrub is calculating the
> checksum for the data on gpt/zfs0, and while that's happening, some
> data is updated by Apache or MySQL, and then checksum for the data on
> gpt/zfs1 is calculated, which now doesn't match, and therefore the
> scrub is reporting an error.  Is that possible?
>
> If that's not it, could this be a bug?  Or should I be worried about
> my SSDs?  What additional data would be helpful for me to share to
> diagnose this?
>
> --
>
> Tim Gustafson
> Technical Lead, Baskin School of Engineering
> tjg@ucsc.edu
> 831-459-5354
> Baskin Engineering, Room 313A
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