linux-ext4 - Re: [patch] ext2/3: document conditions when reliable operation is possible

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Date:	Wed, 26 Aug 2009 01:29:35 +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: Re: [patch] ext2/3: document conditions when reliable operation is
	possible


>>>> "ext3 works on flash and MD RAID5, as long as you do not have
>>>> powerfail" seems to be the accurate statement, and if you don't need
>>>> to protect against powerfails, you can just use ext2.
>>>
>>> Strange how your personal preference is totally out of sync with the
>>> entire enterprise class user base.
>>
>> Perhaps noone told them MD RAID5 is dangerous? You see, that's exactly
>> what I'm trying to document here.
>
> a MD raid array that's degraded to the point where there is no redundancy 
> is dangerous, but I don't think that any of the enterprise users would be 
> surprised.
>
> I think they will be surprised that it's possible that a prior failed  
> write that hasn't been scrubbed can cause data loss when the array later  
> degrades.

Cool, so Ted's "raid5 has highly undesirable properties" is actually
pretty accurate. Some raid person should write more detailed README,
I'd say...
									Pavel

-- 
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