Re: raid is dangerous but that's secret (was Re: [patch] ext2/3:document conditions when reliable operation is possible)

From: david
Date: Sun Aug 30 2009 - 08:56:10 EST

On Sun, 30 Aug 2009, Pavel Machek wrote:

From: Theodore Tso <tytso@xxxxxxx>

To use your ABS brakes analogy, just becase it's not safe to rely on
ABS brakes if the "check brakes" light is on, that doesn't justify
writing something alarmist which claims that ABS brakes don't work
100% of the time, don't use ABS brakes, they're broken!!!!

If it only was this simple. We don't have 'check brakes' (aka
'journalling ineffective') warning light. If we had that, I would not
have problem.

It is rather that your ABS brakes are ineffective if 'check engine'
(RAID degraded) is lit. And yes, running with 'check engine' for
extended periods may be bad idea, but I know people that do
that... and I still hope their brakes work (and believe they should
have won suit for damages should their ABS brakes fail).

the 'RAID degraded' warning says that _anything_ you put on that block device is at risk. it doesn't matter if you are using a filesystem with a journal, one without, or using the raw device directly.

David Lang
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