linux-kernel - Re: MD/RAID: what's wrong with sector 1953519935?

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Message-ID: <4A95573A.6090404@redhat.com>
Date:	Wed, 26 Aug 2009 11:39:38 -0400
From:	Ric Wheeler <rwheeler@...hat.com>
To:	Andrei Tanas <andrei@...as.ca>
CC:	NeilBrown <neilb@...e.de>, linux-kernel@...r.kernel.org,
	linux-ide-owner@...r.kernel.org
Subject: Re: MD/RAID: what's wrong with sector 1953519935?

On 08/26/2009 10:46 AM, Andrei Tanas wrote:
> On Wed, 26 Aug 2009 06:34:14 -0400, Ric Wheeler<rwheeler@...hat.com>
> wrote:
>> On 08/25/2009 11:45 PM, Andrei Tanas wrote:
>>>>>> I would suggest that Andrei might try to write and clear the IO
>>>>>>
>>>> error
>>>>
>>>>>> at that
>>>>>> offset. You can use Mark Lord's hdparm to clear a specific sector or
>>>>>> just do the
>>>>>> math (carefully!) and dd over it. It the write succeeds (without
>>>>>> bumping your
>>>>>> remapped sectors count) this is a likely match to this problem,
>>>>>>
>>>>> I've tried dd multiple times, it always succeeds, and the relocated
>>>>>
>>>> sector
>>>>
>>>>> count is currently 1 on this drive, even though this particular fault
>>>>> happened at least 3 times so far.
>>>>>
>>>>>
>>>> I would bump that count way up (say to 2) and see if you have an
>>>> issue...
>>>>
>>> Not sure what you mean by this: how can I artificially bump the
> relocated
>>> sector count?
>>>
>>>
>> Sorry - you need to set the tunable:
>>
>> /sys/block/mdX/md/safe_mode_delay
>>
>> to something like "2" to prevent that sector from being a hotspot...
>
> I did that as soon as you suggested that it's possible to tune it. The
> array is still being rebuilt (it's a fairly busy machine, so rebuilding is
> slow). I'll monitor it, but I don't expect to see the results soon as even
> with the default value of 0.2 it used to happen once in several weeks.
>
> On the other note: is it possible that the drive was actually working
> properly but was not given enough time to complete the write request? These
> newer drives have 32MB cache but the same rotational speed and seek times
> as the older ones so they must need more time to flush their cache?
>
> Andrei.
>

Timeouts on IO requests are pretty large, usually drives won't fail an IO unless 
there is a real problem but I will add the linux-ide list to this response so 
they can weigh in.

I suspect that the error was real, but might be this "repairable" type of 
adjacent track issue I mentioned before. Interesting to note that just following 
the error, you see that it was indeed the super block that did not get updated...

The error you referenced was:

90307.328266] ata2.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x6
frozen
[90307.328275] ata2.00: cmd ea/00:00:00:00:00/00:00:00:00:00/a0 tag 0
[90307.328277]          res 40/00:01:01:4f:c2/00:00:00:00:00/00 Emask 0x4
(timeout)
[90307.328280] ata2.00: status: { DRDY }
[90307.328288] ata2: hard resetting link
[90313.218511] ata2: link is slow to respond, please be patient (ready=0)
[90317.377711] ata2: SRST failed (errno=-16)
[90317.377720] ata2: hard resetting link
[90318.251720] ata2: SATA link up 3.0 Gbps (SStatus 123 SControl 300)
[90318.338026] ata2.00: configured for UDMA/133
[90318.338062] ata2: EH complete
[90318.370625] end_request: I/O error, dev sdb, sector 1953519935
[90318.370632] md: super_written gets error=-5, uptodate=0


Ric

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