[OpenAFS] [Q] Moving one volume from one cell to other cell

[Steven Jenkins]

On Sat, Mar 14, 2009 at 9:24 AM, Lars Schimmer <l.schimmer@cgv.tugraz.at> wrote:
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> S.J.Chun wrote:
>> Hi,
>>
>> Can I move volume from one cell(original one) to the other cell? We have
>> a fileserver at a.com but we want to move it to b.com cell. Can we just move
>> it by changing ThisCell and sync{serv,vldb} thing?
>
> IMHO best way is to vos dump the volume and vos restore it on the new cell.
>

If you are only moving one volume, the suggestion Lars gave is best.
However, if you need to move an entire server, and you have a large
number of volumes, you could change CellServDB and ThisCell as you
have mentioned, then restart the fileserver and run vos syncvldb for
the fileserver in the new cell; you should also run a script to do the
appropriate vos remove/delentry's from the old cell. A post-move audit
should also be done to verify everything is correct.

Note that this assumes your Kerberos configuration lets you move a
fileserver from one cell to another without reconfiguration (i.e.,
adding new keys, removing old ones).  Also, this does not discuss what
you expect the client behavior to be in with the move -- you'll need
to take some care to ensure you have the right level of availability.
Specifically, you don't mention when and how you want to change the
mountpoints from one cell to another (i.e., before or after doing a
move) -- changing the mountpoints is very important.

The tradeoff between the two processes (vos dump/restore one volume at
a time versus moving an entire fileserver) is a tradeoff between time
and scope of potential outage.  Note that in the vos dump/restore
case, your clients can continue to access the existing server, even
after the dump/restores have taken place.  This may cause consistency
problems with your data.  On the other hand, doing vos dump/restore
limits the scope of a single outage -- problems are likely to be at
the individual volume level, not widespread across the server.

The fileserver reconfiguration, on the other hand, is an
all-or-nothing approach.  An accident or problem could have
significant impact in your environment.

You should consider your needs, and regardless of the option you
choose, you should test the process in a test environment and make
sure you are comfortable with the procedure before trying it in
production.

If I were doing this type of operation for the first time, I would
strongly prefer the single volume at a time approach.  On the other
hand, if I were trying to do large-scale Internet-level storage, I
would spend the time engineering the second approach so that the
operations staff could move a server from one cell to another in an
automated fashion.

-- 
Steven Jenkins
End Point Corporation
http://www.endpoint.com/