How to start celerra replication ?

Question

Hello folks,

i am getting ready to setup replication between CFS14 and NS80. CFS14 is running 5.5.28 and NS80 is running 5.5.30. I will be using version 1 of replicator.

so i am reading "Using Celerra Replicator 5.5" document and it talks about using fs_copy to do your base copy of PFS snapshot ..that makes sense. Then it says to start replication ..ok so far, but then it says to run an incremental fs_copy by using PFS snapshot1 and PFS snapshot2. Why ? I thought once you enable replication it will start pushing new/changed data to the target file system (delta sets), why do i need to run an incremental fs_copy after enabling replication ?

Thank you

nandas · Accepted Answer

To add, typically the initial baseline copy (first fs_copy) of the PFS may take a longer time to complete from source to Destination - thus if the PFS is in use, you 'll have changed data on the PFS.

You start the replication after the first fs_copy is complete and replication process takes care of all delta sets since you started the replication - but in order to copy all the changes in PFS between the first snapshot (the base line copy was done with reference to this) and the moment you start the replication.

Since fs_copy requires the destination FS to be of raw type, the first fs_copy (baseline copy) from snapshot1 is thus used with convert=no option (so that the destination file system does not get converted to uxfs). But the second (incremental) fs_copy converts the destination to uxfs.

By the way - I understand you have the trust relationship setup between control stations as the very first step.

Also, you mentioned that your source side Celerra is running 5.5.28 code but destination is running 5.5.30 code. As I understand, Replication V1 requires both the Celerras to run the same NAS code. So, please check this out.
Thanks,
Sandip

nandas · Answer

The incremental fs_copy is required to copy any changed data between the time when the first snapshot was taken and the time you start the replication. If you have a new filsystem without any data there will be no incremental data - but still it is better to follow the process as you also have to use convert=yes option to convert the raw file system to a uxfs file system with the second fs_copy process. However, you may avoid this step - but you have to ensure that there is no data on the PFS untill you start the replication and you do NOT use the convert=no option with the first fs_copy.

Hope this helps.
Cheers,
Sandip

dynamox · Answer

Also, you mentioned that your source side Celerra is
running 5.5.28 code but destination is running 5.5.30
code. As I understand, Replication V1 requires both
the Celerras to run the same NAS code. So, please
check this out.

can somebody verify that please ? Bill ?

Thank you for your answer Sandip. Now how about this scenario:

1) I have fileA.txt on my source_fs.
2) I create snapshot1 of source_fs and fs_copy to destination_fs.
3) fileA.txt gets modified
4) i start replication
5) fileA.txt gets modified again
6) i create snapshot2 of source_fs and start incremental fs_copy

What's going to happen with fileA.txt ...which fileA.txt will end up on the destination_fs. The one that was modified in step 3 or step 5 ?

Thanks

dynamox · Answer

Munich actually and since Octoberfest is coming up Iguess after a couple of beers you wouldnt notice ifit has loaded yet oh yeah ...Celerra would be the last thing on my mind at that point

dynamox · Answer

Peter ..would you please explain why this would be the case. Does replicator have higher priority over fs_copy ? Or in 'Symm' terms ..that tracks get merged and only the latest change to the file gets applied ? I am just curious how fs_copy and replicator will handle blocks that changed on PFS but have yet to be applied to destination_fs.

dynamox · Answer

Rainer ..by the time i pull up the GUI on CFS14, i will have enough time to fly to Berlin, have a beer
with you and fly back and it will be still loading

Munich actually and since Octoberfest is coming up I guess after a couple of beers you wouldnt notice if it has loaded yet

dynamox · Answer

Also, I'll prefer to engage EMC team before setting
up the replication as your boxes are already in
production.

Sandip ...let me guess your title at EMC ...Manager of Professions services for South-East region

? ...Nahh ..you are too technical to be a manager

dynamox · Answer

I think what happens behind the covers is this

you do the full fs_copy to get the initial data over
there
then you start Replicator, but it will wait since
there could be changes since the start of the full
fs_copy
you start the incremental fs_copy
the replicaton service lurking in the background will
notice as soon as the incremental fs_copy is done and
start maintaining its bitmaps and building savvols

interesting ...so if incremental fs_copy has not been initiated ..you essentially have no replication going on ?

nandas · Answer

The time difference between starting the replication and running the incremental copy with second checkpoint is very less - but still your example is a valid one and in this case, the destination file system will have the latest copy of the file as it was modified by the replication process.

Coming to the NAS code - I am pretty sure you must have exact same version of NAS code running on both the boxes - NOT the same family of code (i mean to say not any combination of 5.5 code but exactly the same code level within 5.5 family).

Also, I'll prefer to engage EMC team before setting up the replication as your boxes are already in production.

I am sure there will be others replying to this post

..
Regards,
Sandip

Rainer_EMC · Answer

you could start Celerra Manager on the NS80 - I dont think direction matters

Rainer_EMC · Answer

I think what happens behind the covers is this

you do the full fs_copy to get the initial data over
there
then you start Replicator, but it will wait since
there could be changes since the start of the full
fs_copy
you start the incremental fs_copy
the replicaton service lurking in the background will
notice as soon as the incremental fs_copy is done and
start maintaining its bitmaps and building savvols

interesting ...so if incremental fs_copy has not been initiated ..you essentially have no replication going on ?

Peter_EMC · Answer

fileA.txt which was modified in step5 will end up in the destination FS.

nandas · Answer

That's nice

.. I wish I have such a big post

.. but unfortunately (or fortunately - it's relative

) I am only a small tech person.

But please don't take me wrong - I know you are technically an expert and very much capable of doing this on your own - but at least keep your EMC team informed about the replication setup. I don't mean to get the service from EMC ($$$$!!!) - but to keep them informed and if possible engaged with consultation/suggestion. In that case, in our Installed base system also, they can add the note that you have Celerra Replicator running on your systems for future references.

By the way - flying to Germany may be much expensive - so you may consider flying down to Austin

Rainer_EMC · Answer

Rainer ..by the time i pull up the GUI on CFS14, i will have enough time to fly to Berlin, have a beer
with you and fly back and it will be still loading

Munich actually and since Octoberfest is coming up I guess after a couple of beers you wouldnt notice if it has loaded yet

Rainer_EMC · Answer

I know you dont like the GUI - but please try it once for this

On setting up a replication it really saves time and patience
It will do all these steps with just a few clicks and you just have to watch nas_tasks to see how it proceeds

Celerra

How to start celerra replication ?

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