[lustre-discuss] lfs_migrate

[Henri Doreau]

On 20/mars - 22:50 E.S. Rosenberg wrote:
> On Mon, Mar 20, 2017 at 10:19 PM, Dilger, Andreas <andreas.dilger at intel.com>
> wrote:
> 
> > The underlying "lfs migrate" command (not the "lfs_migrate" script) in
> > newer Lustre versions (2.9) is capable of migrating files that are in use
> > by using the "--block" option, which prevents other processes from
> > accessing or modifying the file during migration.
> >
> > Unfortunately, "lfs_migrate" doesn't pass that argument on, though it
> > wouldn't be hard to change the script. Ideally, the "lfs_migrate" script
> > would pass all unknown options to "lfs migrate".
> >
> >
> > The other item of note is that setting the OST inactive on the MDS will
> > prevent the MDS from deleting objects on the OST (see
> > https://jira.hpdd.intel.com/browse/LU-4825 for details).  In Lustre 2.9
> > and later it is possible to set on the MDS:
> >
> >    mds# lctl set_param osp.<OST>.create_count=0
> >
> > to stop MDS allocation of new objects on that OST. On older versions it is
> > possible to set on the OSS:
> >
> >   oss# lctl set_param obdfilter.<OST>.degraded=1
> >
> > so that it tells the MDS to avoid it if possible, but this isn't a hard
> > exclusion.
> >
> > It is also possible to use a testing hack to mark an OST as out of inodes,
> > but that only works for one OST per OSS and it sounds like that won't be
> > useful in this case.
> >
> > Cheers, Andreas
> >
> You're making me want Lustre 2.9 more :) but for now I'm still stuck on 2.8
> and because this is very much production these days I'm more careful with
> the update (hoping to finally get hw allocated for a test env soon to test
> the update).
> Thanks,
> Eli
> 

Hello,

this safer version of `lfs migrate' (LU-4840) is actually available in
2.8.

When used with --non-block flag, a concurrent open of the file being
migrated will cause the migration to fail. With --block (or nothing,
it's the default behavior) and as Andreas said, concurrent opens will
block until the migration completes.

Regards

-- 
Henri Doreau