Re: Redundancy check using "echo check > sync_action": error reporting?

[Robin Hill <robin@xxxxxxxxxxxxxxx>]

On Fri Mar 21, 2008 at 07:01:43PM -0400, Bill Davidsen wrote:

> Peter Rabbitson wrote:
>> I was actually specifically advocating that md must _not_ do anything on 
>> its own. Just provide the hooks to get information (what is the current 
>> stripe state) and update information (the described repair extension). The 
>> logic that you are describing can live only in an external app, it has no 
>> place in-kernel.
>
> So you advocate the current code being in the kernel, which absent a 
> hardware error makes blind assumptions about which data is valid and which 
> is not and in all cases hides the problem, instead of the code I proposed, 
> which in some cases will be able to avoid action which is provably wrong 
> and never be less likely to do the wrong thing than the current code?
>
I would certainly advocate that the current (entirely automatic) code
belongs in the kernel whereas any code requiring user
intervention/decision making belongs in a user process, yes.  That's not
to say that the former should be preferred over the latter though, but
there's really no reason to remove the in-kernel automated process until
(or even after) a user-side repair process has been coded.

> Currently the "repair" action (which *is* in the kernel now) takes no 
> advantage of the additional information available in these cases I noted. 
> By what logic do you conclude that the user meant "hide the error" when 
> using the "repair" action? What I propose is never less likely to be 
> correct than what the current code does, why would you not want to improve 
> the chances of getting the repair correct?
>
That is, of course, a separate issue to whether it should be in-kernel.
I would entirely agree that user-level processes should be able to
access and manipulate the low-level RAID data/metadata (via the md
layer) in order to facilitate more advanced repair functions, but this
should be separate from, and in addition to, the "ignorant"
parity-updating repair process currently in place.

Just my 2p,
        Robin
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    ( ' }     |       Robin Hill        <robin@xxxxxxxxxxxxxxx> |
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