[lustre-discuss] lfs_migrate

[Henri Doreau]

Hi,

before people look for the man page in vain: although there is actually
a lfs-migrate(1) man page in 2.8 sources it doesn't seem to be
installed...

Page was added in [1] (included in 2.8) but only added to the
Makefile.am in [2] (which will be part of 2.10).

Regards

Henri

[1] https://review.whamcloud.com/#/c/17392
[2] https://review.whamcloud.com/#/c/24371

On 04/avril - 22:20 Dilger, Andreas wrote:
> There is the "lfs-migrate.1" man page that has a few more details, though it would be great if someone had the time to add more details on each of the options.
> 
> On Apr 4, 2017, at 01:18, Henri Doreau <henri.doreau at cea.fr> wrote:
> > 
> > Hello,
> > 
> > the manpage for lfs(1) lists the available options in 2.8:
> > """
> > lfs migrate -m <mdt_index> directory
> > lfs migrate [-c | --stripe-count <stripe_count>]
> >               [-i | --stripe-index <start_ost_idx>]
> >               [-S | --stripe-size <stripe_size>]
> >               [-p | --pool <pool_name>]
> >               [-o | --ost-list <ost_indices>]
> >               [-b | --block]
> >               [-n | --non-block] file|directory
> > """
> > 
> > Although this is certainly terse, I guess that most parameters are intuitive.
> > 
> > The command will open the file to restripe (blocking concurrent accesses
> > or not, depending on -b/-n), create a special "volatile" (=unlinked) one
> > with the requested striping parameters and copy the source into the
> > destination.
> > 
> > If the copy succeeds, the two files are atomically swapped and
> > concurrent access protection is released.
> > 
> > In non-blocking mode, the process will detect if the source file was
> > already opened or if there's an open during the copy process and abort
> > safely. It is then up to the admin to reschedule the migration later,
> > maybe with -b.
> > 
> > HTH
> > 
> > Henri
> > 
> > On 02/avril - 14:43 E.S. Rosenberg wrote:
> >> Thanks for all the great replies!
> >> 
> >> I may be wrong on this but 'lfs migrate' does not seem to be documented in
> >> the manpage (my local one is 2.8 so I expect that but even manpages that I
> >> find online).
> >> 
> >> Any pointers would be very welcome.
> >> 
> >> On Thu, Mar 23, 2017 at 12:31 PM, Henri Doreau <henri.doreau at cea.fr> wrote:
> >> 
> >>> 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
> >>> 
> 
> Cheers, Andreas
> --
> Andreas Dilger
> Lustre Principal Architect
> Intel Corporation
> 
> 
> 
> 
> 
> 
> 

-- 
Henri Doreau