[lustre-discuss] [HPDD-discuss] possible to read orphan ost objects on live filesystem?

[Martin Hecht]

Hi Chris,

On 09/02/2015 07:18 AM, Chris Hunter wrote:
> Hi Andreas
>
> On 09/01/2015 07:22 PM, Dilger, Andreas wrote:
>> On 2015/09/01, 7:59 AM, "lustre-discuss on behalf of Chris Hunter"
>> <lustre-discuss-bounces at lists.lustre.org on behalf of
>> chris.hunter at yale.edu> wrote:
>>
>>> Hi Andreas,
>>> Thanks for your help.
>>>
>>> If you have a striped lustre file with "holes" (ie. one chunk is gone
>>> due hardware failure, etc.) are the remaining file chunks considered
>>> orphan objects ?
> So when a lustre striped file has a hole (eg. missing chunk due to
> hardware failure), the remaining file chunks stay indefinitely on the
> OSTs.
> Is there a way to reclaim the space occupied by these pieces (after
> recovery of any usuable data, etc.)?
these remaining chunks still belong to the file (i.e. you have the
metadata entry on the MDT and you see the file when lustre is mounted).
By removing the file you free up the space.

In general there are two types of inconsistencies which may occur:
Orphan objects are objects which are NOT assigned to an entry on the
MDT, i.e. chunks which do not belong to any file. These can be either
pre-allocated chunks or chunks left over after a corruption of the
metadata on the MDT.

The other type of corruption is that you have a file, where chunks are
missing in-between. This can happen, when an OST gets corrupted. As long
as the MDT is Ok, you should be able to remove such a file. If in
addition the MDT is also corrupted, you should first fix the MDT, and
you might then only be able to unlink the file (which again might leave
some orphan objects on the OSTs). lfsck should be able to remove them,
depending on the lustre version you are running...

Another point: When the OST got corrupted, after having them repaired
with e2fsck, you can mount them as ldiskfs and see if there are chunks
in lost+found and use the tool ll_recover_lost_found_objs to restore
them in the original place. I believe these objects which e2fsck puts in
lost+found are another kind of thing, usually not called "orphan
objects". As I said, they usually can be easily recovered.

Martin


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