Re: "Unformat" a ReiserFS partition : a testimony :-)

[Yury Umanets <umka@namesys.com>]

Manuel Krause wrote:

> On 03/25/2003 01:16 AM, Yury Umanets wrote:
>
>> Nicolas Vanderavero wrote:
>>
>>> Hello,
>>
>>
>> Hello Nicolas,
>>
>>> while reinstalling a Debian on a new hard drive, I made the mistake 
>>> to format in reiserfs my good old /home which was on /dev/sda7 
>>> instead of formatting the new /dev/hda7. Gasp ! Eight gigabytes lost 
>>> ...
>>>
>>> Or ... maybe it was not totally lost :-) I immediately made a dump 
>>> of the partition with 'dd' and started grepping some known text on 
>>> it. It seemed that no data was really lost. I didn't know what to 
>>> do. So I read the man pages and found the reiserfsck command quite 
>>> interesting :-)
>>
>>
>> You have lost the super block and probably old root node. I said 
>> "probably" because it might be not used in teh time you did format.
>
>
> Can you be more clear on this? In which cases does SB get used? Or, 
> how would this change Nicholas scenario in practical use? E.g. would a 
> blank mount (just mount+umount) change the story so that the partition 
> would not be recoverable? 

I'm sure that usual mount+umount cannot do bad things like this. But why 
did you ask me about that? I mean that Nicolas has explicitly formatted 
his partition by means of using mkreiserfs. And I know that mkreiserfs 
creates new super block at 16 block and also leaf for root node, first 
bitmap and journal.

As old bitmap is corrupted, --rebuild-tree -S will be apparently needed.

>
>
>>>
>>> Ok, I am a total newbie to filesystems and to ReiserFS. So maybe it 
>>> will sound trivial to you, but just in case it happens to anyone 
>>> else, I just wanted to say that running a reiserfsck --rebuild-tree 
>>> -S on my partition was enough to unformat it. I ended up with some 
>>> file in lost+found, but a 'file *' is enough to discover what they are. 
>>
>>
>> The first thing you should do in cases like this is to make backup. I 
>> hope you'll find eight gigabytes for that. Now you may feel free to 
>> do anything with you old partition. Then you should to do 
>> --rebuild-sb and try to fsck the partition with --check key. Then 
>> follow to fsck sugestions.
>>
>> These should be enought for getting you partition back.
>>
>>> So, maybe it would be usefull to add an entry in the "Example of 
>>> using" section of the man page of reiserfsck, saying something like 
>>> : "If you reformatted by mistake a reiserFS partition, you can try 
>>> to unformat it by running reiserfsck --rebuild-tree -S on it". 
>>
>>
>> Sounds good. Probably Vitaly should consider about that for including 
>> it in the next fsck -pre.
>>
>>>
>>> Anyway, thank you for developing this filesystem.
>>> Nicolas Vanderavero.
>>>
>> P.S. Please read http://www.namesys.com/support.html. Can you as for 
>> support? 
>

So the plan is the following:

(1) Backup your data.
(2) Rebuild super block if it had some special like relocated journal.
(3) Rebuild tree with partition scanning --rebuild-tree -S.

This should reanimate your old partition but expect, that you will found 
some of your data in the /lost+found directory.

>
> BTW, I think he found and published a new "feature" (that many would 
> like to have in handy in those cases!) and did *not* ask for support. 
> Shouldn't you pay him 25$, now?! ;-))
>
> Thanks and best regards,
>
> Manuel
>
>
>


-- 
Yury Umanets