linux-ext4 - Re: [PATCH 0/4] (RESEND) ext3[34] barrier changes

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Date:	Wed, 21 May 2008 13:15:12 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Pavel Machek <pavel@...e.cz>, Chris Mason <chris.mason@...cle.com>,
	Theodore Tso <tytso@....edu>, Andi Kleen <andi@...stfloor.org>,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 0/4] (RESEND) ext3[34] barrier changes

Andrew Morton wrote:
> On Wed, 21 May 2008 13:22:25 +0200 Pavel Machek <pavel@...e.cz> wrote:

>>> I tested this one with a larger FS (40GB instead of 2GB) and larger log (128MB 
>>> instead of 32MB).  barrier-test -s 32 -p 1500 was still able to get a 50% 
>>> corruption rate on the larger FS.
>> Ok, Andrew, is this enough to get barrier patch applied and stop
>> corrupting data in default config, or do you want some more testing?
>>
>> I guess 20% benchmark regression is bad, but seldom and impossible to
>> debug data corruption is worse...
> 
> It is 20%?  I recall 30% from a few years ago, but that's vague and it
> might have changed.  Has much quantitative testing been done recently? 
> I might have missed it.
> 
> If we do make this change I think it should be accompanied by noisy
> printks so that as many people as possible know about the decision
> which we just made for them.
> 
> afaik there is no need to enable this feature if the machine (actually
> the disks) are on a UPS, yes?

As long as your power supply (or your UPS) doesn't go boom, I suppose so.

It is too bad that there is no way to determine no-barrier safety from
software.  (maybe apcupsd could do something... ;)

I guess it's levels of confidence.  I agree that a user education
campaign is probably in order... maybe if this thread is long enough to
make LWN it'll raise some awareness.  :)

-Eric
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