Re: Force parity resync on raid5?

[David Greaves <david@dgreaves.com>]

what about
n=0
while
  dd if=/dev/md0 of=/tmp/block count=x_for_efficiency seek=n
  dd of=/dev/md0 if=/tmp/block count=x_for_efficiency seek=n
  n=n+1
loop

?

This would read the good data and force a rewrite - would you need to 
stop any optimisers?

David

Guy wrote:

>Ouch!  No!!
>
>This would re-build data from parity!!!
>He thinks his parity is bad.
>He wants to re-build the parity from the data!
>I don't know if this can even be done!
>Recovering from a power failure does force a re-build (2.4), but from what I
>remember the system looks like it is re-building a failed disk, which is not
>what he wants to do.  If the parity was good, re-building any 1 disk would
>be fine.
>
>Guy
>
>-----Original Message-----
>From: linux-raid-owner@vger.kernel.org
>[mailto:linux-raid-owner@vger.kernel.org] On Behalf Of Gordon Henderson
>Sent: Tuesday, August 10, 2004 5:04 AM
>To: Philip Molter
>Cc: linux-raid@vger.kernel.org
>Subject: Re: Force parity resync on raid5?
>
>On Mon, 9 Aug 2004, Philip Molter wrote:
>
>  
>
>>How do I force a parity resync on a raid5 array?  Under 2.4, I would do
>>this by hard cycling the box and when it came back up, it would
>>automatically resync the array.  Under 2.6, this appears to have gone
>>    
>>
>away.
>
>I don't know about 2.6, (still living with 2.4) but can't you simply do:
>
>  raidhotremove /dev/mdX /dev/hdYZ
>
>followed by
>
>  raidhotadd /dev/mdX /dev/hdYZ
>
>or /dev/sdYZ if SCSI disks...
>
>However, picking the right disk to remove might be tricky... And if you
>were at all unsure about data on the disks, maybe rebooting and doing a
>hard fsck of the partition(s) in maintenance mode might be a good thing
>too...
>
>Good luck!
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>  
>