linux-kernel - Re: [PATCH 26/30] ext4: do not send discards as barriers

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Message-ID: <20100830210205.GD12226@quack.quadriga.com>
Date:	Mon, 30 Aug 2010 23:02:05 +0200
From:	Jan Kara <jack@...e.cz>
To:	Vladislav Bolkhovitin <vst@...b.net>
Cc:	Jan Kara <jack@...e.cz>, Jeff Moyer <jmoyer@...hat.com>,
	Tejun Heo <tj@...nel.org>, Christoph Hellwig <hch@....de>,
	jaxboe@...ionio.com, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-ide@...r.kernel.org, linux-raid@...r.kernel.org,
	James.Bottomley@...e.de, tytso@....edu, chris.mason@...cle.com,
	swhiteho@...hat.com, konishi.ryusuke@....ntt.co.jp,
	dm-devel@...hat.com, rwheeler@...hat.com, hare@...e.de,
	neilb@...e.de, rusty@...tcorp.com.au, mst@...hat.com,
	jeremy@...p.org, snitzer@...hat.com, k-ueda@...jp.nec.com,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH 26/30] ext4: do not send discards as barriers

On Tue 31-08-10 00:39:41, Vladislav Bolkhovitin wrote:
> Jan Kara, on 08/31/2010 12:20 AM wrote:
> >On Mon 30-08-10 15:56:43, Jeff Moyer wrote:
> >>Jan Kara<jack@...e.cz>  writes:
> >>
> >>>   An update: I've set up an ext4 barrier testing in KVM - run fsstress,
> >>>kill KVM at some random moment and check that the filesystem is consistent
> >>>(kvm is run in cache=writeback mode to simulate disk cache). About 70 runs
> >>
> >>But doesn't your "disk cache" survive the "power cycle" of your guest?
> >   Yes, you're right. Thinking about it now the test setup was wrong because
> >it didn't refuse writes to the VM's data partition after the moment I
> >killed KVM. Thanks for catching this. I will probably have to use the fault
> >injection on the host to disallow writing the device at a certain moment.
> >Or does somebody have a better option?
> 
> Have you considered to setup a second box as an iSCSI target (e.g.
> with iSCSI-SCST)? With it killing the connectivity is just a matter
> of a single iptables command + a lot more options.
  Hmm, this might be an interesting option. Will try that. Thanks for
suggestion. 

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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