Re: Help with data recovery - RAID6 with 2 failed drives and another with broken sectors

[Phil Turmel <philip@turmel.org>]

Hi Michał,

On 10/01/2013 03:24 PM, Michał Sawicz wrote:
> On 01.10.2013 01:23, Michał Sawicz wrote:

[trim /]

>> What I'd like to do first is to make sure the array rebuilds onto the 6
>> healthy drives, regardless of the bad blocks, I can probably recover the
>> data (assuming I can find out which files were affected - any
>> pointers?), but if the array doesn't rebuild correctly, I'm afraid it's
>> gonna get worse, and soon.
> 
> OK, so a ddrescue and --zero-superblock later my array is rebuilding
> onto one healthy spare. According to ddrescue I only lost some 8kB of
> data in more or less one chunk, so after the array is rebuilt my next
> task will be finding which file(s) that was.

I noticed that you never got any direct response, and I realized you
might still be at risk.  In particular, your OP said:

> As a side note... I've a full array scrub enabled on the array every now
> and again - and it did run after the disk started failing blocks, but
> they never got reallocated, they all remain pending / uncorrectable. Is
> that expected?

The answer is *NO*.  That is not expected.  But it does happen with
timeout mismatches, and the double failure you experienced is a common
result of error correction timeout mismatch.  Timeout mismatch is where
your drives are internally trying to retry reading a bad sector long
after the OS has given up.  It is always associated with consumer-grade
hard drives in raid arrays.

You might want to search the list archives for various combinations of
"error recovery", "scterc", "URE" and "timeout mismatch" for a full
description of the problem and the recommended ways to avoid it.

HTH,

Phil

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