[Lustre-discuss] question about size on MDS (MDT) for lustre-1.8

[Nathan Dauchy]

Revisiting this thread after 2 months...

On 01/12/2011 05:45 PM, Robin Humble wrote:
> On Thu, Jan 06, 2011 at 05:42:24PM -0700, Nathan.Dauchy at noaa.gov wrote:
>> I am looking for more information regarding the "size on MDS" feature as
>> it exists for lustre-1.8.x.  Testing on our system (which started out as
>> 1.6.6 and is now 1.8.x) indicates that there are many files which do not
>> have the size information stored on the MDT.  So, my basic question:
>> under what conditions will the "size hint" attribute be updated?  Is
>> there any way to force the MDT to query the OSTs and update it's
>> information?
> 
> atime (and the MDT size hint) wasn't being updated for most of the 1.8
> series due to this bug:
>   https://bugzilla.lustre.org/show_bug.cgi?id=23766
> the atime fix is now in 1.8.5, but I'm not sure if anyone has verified
> whether or not the MDT size hint is now behaving as originally intended.

I wanted to report back that I applied the patch in that bug and it
appears as though the MDT size hint is working.  This is tested with
lustre-1.8.4.ddn2.2 and linux-2.6.18-194.32.1 on the MDS.

> BTW, once you have 1.8.5 on the MDS, then a hack to populate the MDT
> size hints might be to read 4k from every file in the system. that
> should update atime and the size hint. please let us know if this works.
> 

Yes, performing "ls -l" on the file from the client was not sufficient.
 The size hint was updated on the MDS after reading 1k from the file on
the client.  Running 'du --apparent-size' now reports the exact same
value on the MDT snapshot as on the client.

-Nathan