[lustre-discuss] lfs_migrate

[Dilger, Andreas]

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