Re: xfs_repair force_geometry

[Benedikt Schmidt <benedikt.schmidt@tum.de>]

On 14.05.2013 09:50, Michael L. Semon wrote:
> On 05/14/2013 01:11 AM, Benedikt Schmidt wrote:
>> First of all: Thanks for your very fast and helpful response.
>>
>> I copied actually only the partition, not the whole disk: /dd_rescue
>> --force -r1 /dev/sdd1 /dev/sdc1/
>> The cause for this is that I don't have enough space left on another
>> device to store a whole copy of the faulty disk. I thought it would be
>> possible, like in some examples I found with google, that you can rescue
>> a partition directly.
>
> Understood.  This seems like a valid option.  Had fdisk, cfdisk, and 
> gdisk been more cooperative over the past year, this would have been 
> my first option.
>
>> /file -s /dev/sdc1/ says:
>> //dev/sdc1: data/
>
> This is different from what I got, but maybe Eric sees something in 
> your answer.
>
>> The disks look like this (/fdisk -l/):
>> /Disk /dev/sdc: 3000.6 GB, 3000592982016 bytes, 5860533168 sectors//
>> //Units = Sektoren of 1 * 512 = 512 bytes//
>> //Sector size (logical/physical): 512 bytes / 4096 bytes//
>> //I/O size (minimum/optimal): 4096 bytes / 4096 bytes//
>> //Disk identifier: 0xcba506ee//
>> //
>> //   Gerät  boot.     Anfang        Ende     Blöcke   Id System//
>> ///dev/sdc1             256   732566645   366283195   83 Linux//
>> //
>> //Disk /dev/sdd: 2000.4 GB, 2000397852160 bytes, 3907027055 sectors//
>> //Units = Sektoren of 1 * 512 = 512 bytes//
>> //Sector size (logical/physical): 512 bytes / 512 bytes//
>> //I/O size (minimum/optimal): 512 bytes / 512 bytes//
>> //Disk identifier: 0x3c34826b//
>> //
>> //   Gerät  boot.     Anfang        Ende     Blöcke   Id System//
>> ///dev/sdd1              63  3907024064  1953512001   83 Linux/
>>
>> If it is not possible to rescue the partition this way I will have to
>> extend my to RAID5 so that I can put the copy of the faulty disk on this
>> one, like Michael explained in his answer. I just hoped that I can avoid
>> this, because it would save me more than 100€.
>
> I had not much information to use, so I set up the safest possible 
> scenario and hoped that you were getting results that were close to that.
>
> If the few extra files that you're rescuing aren't worth 100 euros, 
> then it's not worth 100 euros to make a duplicate of a dump of an 
> already-damaged filesystem.
>
> The crazy, reckless guide is this:
>
> 1) use `xfs_repair -n /dev/sdc1`.  If that looks nice,...
>
> 2) use `xfs_repair /dev/sdc1`...
>
>   a) A repaired partition is a good sign.  Mount that partition!
>
>   b) If the "attempting to find secondary superblock" search ends in 
> "Sorry, could not find valid secondary superblock," then maybe 
> something went wrong in the original data transfer.  You might have to 
> give this step some time to complete, and it will print dots for a 
> while.  Either that or the failures in your hard drive really did hit 
> all of the superblocks.
>
>   c) If the "attempting to find secondary superblock" finds something, 
> it might make everything well but spit some files into lost+found.  If 
> the repair goes badly, there's a chance you'll be using dd to look for 
> your data.
>
>   d) If it's something else--xfs_repair segfaults, needs to be run 
> again, whatever, mention it--and at least you'll be closer to the real 
> answer.
>
> 3) If all else fails, and especially when a backup is handy, you could 
> try `xfs_repair -L` to zero the log.  This helps when xfs_repair asks 
> you to mount the filesystem to allow metadata updates to happen, but 
> Linux has an oops as the filesystem is mounted.  In many other 
> scenarios, it can work against you.  This is the second-to-last resort.
>
>> As last information: The content of this copy is not totally lost,
>> actually only the last few files I have added. All the other stuff is
>> already stored on the RAID5, only the latest stuff is not contained in
>> this backup. So I don't loose everything if something goes wrong (at
>> least one thing :-) ).
>
> Really, it becomes a question of whether it would be faster to search 
> for the data using dd and grep, use xfs_repair and hope it works, or 
> recreate the data from scratch.
>
> The hope is that dd_rescue does a credible job for you, and that XFS 
> can be made to mount something, somewhere, so that you can grab those 
> last few files.  The very last resort would be to do all of this 
> repair stuff on the original damaged partition, but the safety net 
> goes away after that.
>
> Michael

I see, I should have mentioned this earlier. I already tried xfs_repair 
and it failed to find the second superblock. Because I am still able to 
mount the original disk and most parts of it I guessed that xfs_repair 
is confused by the different disk geometries. What I have also already 
tried out was, naturally, to copy the whole stuff with for example cp or 
xfs_copy, but both failed because of filesystem errors. The only program 
which didn't fail to copy the data was dd_rescue, which can handle the 
errors. That is why I used, as it was my only option (as far as I can see).

Kind regards,
Benedikt

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