[lustre-discuss] OST -> MDT migration and MDT -> OST migration

[Andreas Dilger]

On Apr 15, 2021, at 00:52, Åke Sandgren <ake.sandgren at hpc2n.umu.se> wrote:
> 
> 
> 
>> On 4/15/21 5:12 AM, Andreas Dilger via lustre-discuss wrote:
>> On Apr 14, 2021, at 18:42, Bill Anderson via lustre-discuss
>> <lustre-discuss at lists.lustre.org
>> <mailto:lustre-discuss at lists.lustre.org>> wrote:
>>> 
>>> 
>>>    Hi All,
>>> 
>>>    I'm trying to figure out how to migrate files stored on an OST to
>>> an MDT (that's using DoM) and to migrate files stored on an MDT to an
>>> OST (e.g., if the MDT is getting full).  I can see how to migrate
>>> between OSTs, but not between OSTs and MDTs.  I'm running Lustre 2.12.3.
>>> 
>>>  Do you happen to know the syntax for migration between OSTs and MDTs?
>>> 
>>>    Thanks for any help!
>> 
>> You just use "lfs migrate <file layout> <file>" to migrate from DoM
>> files to OST objects.  However, OST-to-DoM migration isn't available
>> until 2.13.
> 
> Couldn't you just use lfs mirror extend with a PFL that points into the
> DoM, and then a resync/split

Yes, and that's what happens in 2.13 when this functionality is
implemented. To migrate from DoM->OST you can just make a copy of
the file and swap layouts. The issue in 2.12 is that you can't write into the
MDT inode to do OST->DoM migration/mirroring. 

Cheers, Andreas