On 2010-11-06, at 8:24, Bob Ball <[email protected]> wrote:
> I am emptying a set of OST so that I can reformat the underlying RAID-6 
> more efficiently.  Two questions:
> 1. Is there a quick way to tell if the OST is really empty?  lfs_find 
> takes many hours to run.

If you mount the OST as type ldiskfs and look in the O/0/d* directories 
(capital-O, zero) there should be a few hundred zero-length objects owned by 
root.

> 2. When I reformat, I want it to retain the same ID so as to not make 
> "holes" in the list.  From the following information, am I correct to 
> assume that the id is 24?  If not, how do I determine the correct ID to 
> use when we re-create the file system?

If you still have the existing OST, the easiest way to do this is to save the 
files last_rcvd, O/0/LAST_ID, and CONFIGS/*, and copy them into the reformatted 
OST. 

> /dev/sdj              3.5T  3.1T  222G  94% /mnt/ost51
>  10 UP obdfilter umt3-OST0018 umt3-OST0018_UUID 547
> umt3-OST0018_UUID           3.4T        3.0T      221.1G  88% 
> /lustre/umt3[OST:24]
>  20 IN osc umt3-OST0018-osc umt3-mdtlov_UUID 5

The OST index is indeed 24 (18 hex). As for /dev/sdj, it is hard to know from 
the above info. If you run "e2label /dev/sdj"  the filesystem label should 
match the OST name umt3-OST0018. 

Cheers, Andreas
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