[Lustre-discuss] Object index

Andreas Dilger adilger at whamcloud.com
Tue Jul 24 11:10:16 PDT 2012

On 2012-07-24, at 5:04, DEGREMONT Aurelien <aurelien.degremont at cea.fr> wrote:
> I'm trying to analyze an OST with few thousands of object and find where they belong to.
> Mounting this OST with ldiskfs and using ll_decode_filter_fid tells me that.
> -Most of these object do not have a fid EA back pointer. Does that means they are not used?

Two possibilities:
- object is in use, but has never been accessed, maybe because it is stripe N, in a file < N MB in size
- object is preallocated and is not in use yet

In first case (unaccessed object), new lfsck will add parent FID back pointer as part of current Phase II project. 

> -Some of them have good results, and the man page says that
> "For objects with MDT parent sequence numbers above 0x200000000, this indicates that the FID needs to be mapped via the 
> MDT Object Index (OI) file on the MDT".
> How do I do this mapping? I found some iam utilities but they do not seems to be ok, and I'm afraid IAM userspace code 
> has been deactivated.

Using normal "lfs fid2path {FID}" command.

Cheers, Andreas

> How can I know if those files could be removed without risk.
> I previously checked that "lfs find" did not find any other files with object on this specific OST I'm working on.
> Thanks
> Aurélien Degrémont
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