linux-ext4 - [testcase] test your fs/storage stack (was Re: [patch] ext2/3: document conditions when reliable operation is possible)

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Date:	Sat, 29 Aug 2009 11:49:20 +0200
From:	Pavel Machek <pavel@....cz>
To:	david@...g.hm
Cc:	Ric Wheeler <rwheeler@...hat.com>, Theodore Tso <tytso@....edu>,
	Florian Weimer <fweimer@....de>,
	Goswin von Brederlow <goswin-v-b@....de>,
	Rob Landley <rob@...dley.net>,
	kernel list <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>, mtk.manpages@...il.com,
	rdunlap@...otime.net, linux-doc@...r.kernel.org,
	linux-ext4@...r.kernel.org, corbet@....net
Subject: [testcase] test your fs/storage stack (was Re: [patch] ext2/3:
	document conditions when reliable operation is possible)


>> So instead of fixing or at least documenting known software deficiency
>> in Linux MD stack, you'll try to surpress that information so that
>> people use more of raid5 setups?
>>
>> Perhaps the better documentation will push them to RAID1, or maybe
>> make them buy an UPS?
>
> people aren't objecting to better documentation, they are objecting to  
> misleading documentation.

Actually Ric is. He's trying hard to make RAID5 look better than it
really is.

> for flash drives the danger is very straightforward (although even then  
> you have to note that it depends heavily on the firmware of the device,  
> some will loose lots of data, some won't loose any)

I have not seen one that works :-(.

> you are generalizing that since you have lost data on flash drives, all  
> flash drives are dangerous.

Do the flash manufacturers claim they do not cause collateral damage
during powerfail? If not, they probably are dangerous.

Anyway, you wanted a test, and one is attached. It normally takes like
4 unplugs to uncover problems.

> but the super simplified statement you keep trying to make is  
> significantly overstating and oversimplifying the problem.

Offer better docs? You are right that it does not lose whole stripe,
it merely loses random block on same stripe, but result for journaling
filesystem is similar.
									Pavel


-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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