Re: On URE and RAID rebuild - again!

[Gionatan Danti <g.danti@assyoma.it>]

On 03/08/2014 05:48, NeilBrown wrote:

> You are very unlikely to see UREs just be reading the drive over and over a
> again.  You easily do that for years and not get an error.  Or maybe you got
> one just then.

True. I read over 40 TB from this disk and I haven't find any error. 
Some SMART attribute reported so far:
ID  NAME                    FLAG     V     W     T      R
197 Current_Pending_Sector  0x0012   100   100   000    0
198 Offline_Uncorrectable   0x0010   100   100   000    0

As you can find, no error was reported, and I don't find anything 
suspicious in dmesg. At least, this should prove that article as this 
[1] are quite wrong.

Maybe URE errors are related to unsuccessful writes in the first place. 
I will try to repeat the test intermixing read with full-disk writes.


[1] 
http://subnetmask255x4.wordpress.com/2008/10/28/sata-unrecoverable-errors-and-how-that-impacts-raid/

> If you want to see how the system responds when it hits a URE, you can use the
> hdparm command and the "--make-bad-sector" option.  There is also a
> "--repair-sector" option which will (hopefully) repair the sector when you
> are done.
>
> NeilBrown
>
>
>>
>> Thanks.
>>
>> Il 2014-07-31 09:16 Gionatan Danti ha scritto:
>>>> Yes, you can usually get your data back with mdadm.
>>>>
>>>> With latest code, a URE during recovery will cause a bad-block to be
>>>> recorded
>>>> on the recovered device, and recovery will continue.  You end up with
>>>> a
>>>> working array that has a few unreadable blocks on it.
>>>>
>>>> NeilBrown
>>>
>>> This is very good news :)
>>> I case of parity RAID I assume the entire stripe is marked as bad, but
>>> with mirror (eg: RAID10) only a single block (often 512B) is marked
>>> bad on the recovered device, right?
>>>
>>>  From what mdadm/kernel version the new behavior is implemented? Maybe
>>> the software RAID on my CentOS 6.5 is stronger then expected ;)
>>>
>>> Regards.
>>
>

-- 
Danti Gionatan
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