CentOS - Jun 2011 - what is difference between "slow initialize" and "patrol read" on RAID?

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"?

Thanks.

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"?
>
No, but let me suggest to you that "media error" means just that, a
bad
drive.

       mark

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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> 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
Yes, both can be true. I guess it's simply because a disk which writes on
a bad sector/block just silently remaps it and goes on because it's
considered fixed.
>  * 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
I always tought patrolread just tries to read the whole disk to detect
sleeping bad sectors/blocks. Maybe it also checks consistency on the RAID
level but I'm not sure.

Simon