[Lustre-discuss] questions about an OST content

[Bob Ball]

Responding to everyone....  (and thanks to all)

lfs df -i from a client or simply df -i from the OSS node ...
This still shows of order 100 inodes after the OST was emptied.

"tunefs.lustre --print /dev/sdj" will tell you the index in base 10.
Yes, this worked.

df -H /path/to/OST/mount_point
This still shows several hundred MB as well, in disparate amounts per 
OST I'm emptying.  An indicator, but not perfect.  Yes, the OST were 
near full to begin with.

More below.

On 11/6/2010 11:09 AM, Andreas Dilger wrote:
> On 2010-11-06, at 8:24, Bob Ball<ball at umich.edu>  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.
I assume this is ALL I should see.  Certainly the used inode count 
agrees with this. I will look shortly.

>> 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.
I will do that, thanks.
>> /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.
I intend to be VERY careful with this.  Thank you all.  Any further 
advice before I do this, likely on Monday, will be greatly appreciated.

bob
> Cheers, Andreas
>