Re: [patch] document flash/RAID dangers

[Pavel Machek]

On Tue 2009-08-25 16:56:40, david@xxxxxxx wrote:
> On Wed, 26 Aug 2009, Pavel Machek wrote:
>
>> There are storage devices that high highly undesirable properties
>> when they are disconnected or suffer power failures while writes are
>> in progress; such devices include flash devices and MD RAID 4/5/6
>> arrays.
>
> change this to say 'degraded MD RAID 4/5/6 arrays'
>
> also find out if DM RAID 4/5/6 arrays suffer the same problem (I strongly 
> suspect that they do)

I changed it to say MD/DM.

> then you need to add a note that if the array becomes degraded before a  
> scrub cycle happens previously hidden damage (that would have been  
> repaired by the scrub) can surface.

I'd prefer not to talk about scrubing and such details here. Better
leave warning here and point to MD documentation.

>> THESE devices have the property of potentially corrupting blocks being  
>> written at the time of the power failure,
>
> this is true of all devices

Actually I don't think so. I believe SATA disks do not corrupt even
the sector they are writing to -- they just have big enough
capacitors. And yes I believe ext3 depends on that.
								Pavel
-- 
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