From owner-freebsd-stable@freebsd.org  Mon Nov 21 18:16:28 2016
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Subject: Re: Help! two machines ran out of swap and corrupted their zpools!
To: freebsd-stable@freebsd.org
References: <E1c8sgj-0003Q2-It@dilbert.ingresso.co.uk>
From: Volodymyr Kostyrko <arcade@b1t.name>
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Date: Mon, 21 Nov 2016 20:16:16 +0200
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Pete French wrote:
> So, I am off sick and my colleagues decided to load test our set of five
> servers excesively. All ran out of swap. So far so irritating, but whats has
> happened is that twoof them now will not boot, as it appears the ZFS pool
> they are booting from has become corrupted.
>
> One starts to boot, then crases importing the root pool. The other doenst
> even get that far with gptzfsboot saying it can't find the pool to boot from!
>
> Now I can recover these, but I am a bit worried, that it got like this at
> all, as I havent ever seen ZFS corrupt a pool like this. Anyone got any insights,
> or suggstions as to how to stop it happening again ?
>
> We are swapping to a separate partition, not to the pool by theway.

Good.

Try downloading live disc or mfsBSD and importing pool r/o from there.

zpool import -N -O readonly=on -f -R /mnt/somezpoool

If that doesn't help try:

zpool import -N -O readonly=on -f -R /mnt/somezpoool -Fn

Drop us a line of your configuration and used ZFS features. Like dedup, 
snapshots, external l2 logs and caches.

-- 
Sphinx of black quartz judge my vow.