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Date:      Mon, 07 Jun 2010 14:43:32 +0300
From:      Andriy Gapon <avg@icyb.net.ua>
To:        Jeremy Chadwick <freebsd@jdc.parodius.com>
Cc:        freebsd-fs@freebsd.org
Subject:   Re: zfs i/o error, no driver error
Message-ID:  <4C0CDB64.6090304@icyb.net.ua>
In-Reply-To: <20100607103829.GA50106@icarus.home.lan>
References:  <4C0CAABA.2010506@icyb.net.ua> <20100607083428.GA48419@icarus.home.lan> <4C0CB3FC.8070001@icyb.net.ua> <20100607090850.GA49166@icarus.home.lan> <4C0CBBCA.3050304@icyb.net.ua> <20100607103829.GA50106@icarus.home.lan>

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on 07/06/2010 13:38 Jeremy Chadwick said the following:
> My understanding is that a "vdev I/O error" indicates some sort of
> communication failure with a member in the pool, or some other layer
> within FreeBSD (GEOM I think, like you said).  I don't think there has
> to be a 1:1 ratio between vdev I/O errors and controller/disk errors.
> 
> For AHCI and storage controllers, I/O errors are messages that are
> returned from the controller to the OS, or from the disk through the
> controller to the OS.  I suppose it's possible ZFS could be throwing
> an error for something that isn't actually block/disk-level.
> 
> I'm interested to see what this turns out to be!

Yes, me too :)
I skimmed through the sources and so far I see at least two possibilities:
1) Decompression error for a filesystem with compression.
Again, I don't know why that could happen if there are no checksum errors or
hardware errors.
2) Successful but short read from disk.
Same thing - I don't know why that could happen.

And I am sure that there are other possibilities too.

-- 
Andriy Gapon



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