[CentOS] what is difference between "slow initialize" and "patrol read" on RAID?

Wed Jun 8 20:38:58 UTC 2011
Peter Kjellström <cap at nsc.liu.se>

On Wednesday, June 08, 2011 09:00:48 PM mcclnx mcc wrote:
> We have DELL server with MD1000 Disk array in it.  O.S. is CENTOS 5.5. 
> Recently every time MD1000 "patrol read" start I will get "media error"
> messages on /var/log/message file.
> 
> I use MD1000 "slow initialize" to initialize "bad disk" and NO error. 
> After "slow initialize" finish, I manually "startup patrol read".  I
> continue get "media error" on /var/log/message.
> 
> Anyone know what difference between "slow initialize" and "patrol read"?

Only Dell really knows what they mean by it.

But here are some random thoughts:

 * Slow init may write all of the disk during init but maybe:
  1) no errors happen during write
  2) it notices an error but retries silently
  3) it notices an error but has sucky error reporting
 * Patrolread (may) compare parity data and report this as "media error"
   (a type of error slow init probably wouldn't detect)
 * The I/O pattern of patrolread compared to slow init provoks an error

You could try to take this issue over to the poweredge-linux mailing list or 
just case the bad drive with dell support.

/Peter
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