Re: How to force rewrite of a smart detected bad block with raid5: checkarray?

[NeilBrown <neilb@suse.de>]

On Wed, 19 Jan 2011 09:31:50 -0800 Marc MERLIN <marc@merlins.org> wrote:

> On Wed, Jan 19, 2011 at 08:41:15PM +1100, NeilBrown wrote:
> > All you need to do is get md/raid5 to try reading the bad block.  Once it does
> > that it will get a read error and automagically try to correct it.
>  
> So, if I get this right, raid5 only reads n-1 drives. Unless I'm unlucky
> enough to have the bad disk be the parity stripe, just reading the file with
> a bad stripe by luck would cause the kernel to recompute parity on the read
> error and re-write the bad block?
> (I also read in the online docs that raid4 actually reads all the blocks,
> including parity, which is a bit slower, but would actually guarantee that
> all blocks are read, and parity is still consistent at ready time?)
> 
> 
> But back to your point: check, which I had started, will indeed do what I
> was hoping it would, thanks.
> 
> > If you were really keen, you could 
> >   cd /sys/block/mdXX/md
> >   echo 3907029168 > sync_min
> >   echo 3907029170 > sync_max
> >   echo check > sync_action
> 
> I stopped the full check, and tried:
>  
> gargamel:/sys/block/md7/md# cat sync_min
> 244188936
> gargamel:/sys/block/md7/md# cat sync_max
> max
> gargamel:/sys/block/md7/md# echo 3907029168 > sync_min
> bash: echo: write error: Invalid argument
> 
> Any idea what went wrong here?

Like I suggest, rounding might be necessary.
I just checked the code and this number does need to be a multiple of the
chunk size, which is 1024 sectors for you.
so 
   echo 3907028992 > sync_min

should do the trick.

NeilBrown