[Lustre-discuss] Could I restore OST without EA ?

[Dilger, Andreas]

On 2015/03/11, 12:57 AM, "Tung-Han Hsieh" <thhsieh at twcp1.phys.ntu.edu.tw>
wrote:

>Dear Dilger and All,
>
>Thanks very much for your helpful information.
>
>Now after a long delay, our corrupted data in that OST is rescued
>by a company. We have prepared a new file server, with rebuit RAID
>and Lustre file system (OST), and sent it the the data rescue company
>to copy the data back.
>
>It seems that > 99.9% data files in that OST can be retrived and
>are in their correct O/0/d*/ directories. So later we will try to
>put it back to our Lustre filesystem, and see whether only the EA's
>of MDT could access these files or not.
>
>But here we encounter a problem. Since the facilities of the data
>rescue company is Windows based, they told me that the most they
>can do is to recover the data files, but without all the informations
>of their corresponding inodes (they don't have the tools to do that).
>That means, the owners, creation/modification times, permissions, and
>EA's of all the files can not be recovered. Now we hope that without
>EA's these files can still be accessable. But we still have to fix
>the problems of the owners, creation times, and permissions.

None of these attributes are needed for the OST to work.

>Is it possible that, using the EA's of MDT, could we figure out the
>location of each file ? I mean, could we find, for example, the
>location of
>
>	MDT:  /ROOT/the/full/path/to/a/file
>
>that is in which OST and which file ? Then we can manually fix their
>owner, creation / modification time, and permission manually, according
>to those of the corresponding file in MDT.

With Lustre 2.6 and later, LFSCK will automatically repair these
attributes,
and without them it is not very easy to do this.

Cheers, Andreas

>Thank you very much for your great help.
>
>
>Best Regards,
>
>T.H.Hsieh
>
>
>On Fri, Feb 13, 2015 at 06:09:46PM +0000, Dilger, Andreas wrote:
>> On 2015/02/12, 2:47 AM, "Tung-Han Hsieh" <thhsieh at twcp1.phys.ntu.edu.tw>
>> wrote:
>> 
>> >We have a Lustre filesystem (version 1.8.8) in our lab, which
>> >contains several about 20 OSTs and only one MDT. Recently one
>> >of our file server got serious crashed. It contains 4 OSTs
>> >stored in RAID 5. We sent the file server to data rescue company.
>> >They told me that they can rescue all the data files, but the EA
>> >of these files may be lost.
>> >
>> >In the Lustre Operational Manual, I learn that to restore the
>> >MDT in filesystem level, we should restore both all the files
>> >as well as their EAs. But how about OST ? Could we restore it
>> >without the EA of files ? I mean, without running this ?
>> >
>> >	setfattr --restore=ea.bak
>> >
>> >If very fortunately I can restore it without EA, what is the
>> >next I should do to bring the whole filesystem to be in a
>> >consistant state ?
>> 
>> That depends on whether there is other corruption in the OST
>>filesystems.
>> You do not need the OST EAs for normal usage, but if the OST directory
>> structure is corrupted then the EA data is useful to rebuild the OST
>> directory structure (use ll_recover_lost_found_objs to move objects from
>> lost+found/ into O/0/d*/ directories).
>> 
>> Cheers, Andreas
>> -- 
>> Andreas Dilger
>> 
>> Lustre Software Architect
>> Intel High Performance Data Division
>> 
>> 
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Cheers, Andreas
-- 
Andreas Dilger

Lustre Software Architect
Intel High Performance Data Division