[Lustre-discuss] Object index

Daniel Kobras kobras at linux.de
Tue Jul 24 11:10:55 PDT 2012

Hi Aurelien!

Am 24.07.2012 um 14:04 schrieb DEGREMONT Aurelien:

> 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?

Is this the troglodyte type of OST that started its life in times of prehistoric versions of Lustre? We see this on old files that were created in the early ages of Lustre 1.6, before the trusted.fid EA was introduced. Other than that, these objects could have been preallocated, but never actually used. Do these objects contain any data at all (blockcount != 0)?

> -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.

lfs fid2path (on any client) should do what you're looking for.

> 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.

From my experience, a small amount of object leakage is not too uncommon on real-world systems, so if lfs find doesn't show up any objects anymore, most likely you're good to take this OST down. (Hey, and you can double-check with rbh-report --dump-ost, of course! ;-)



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