[Lustre-discuss] Will it be possible for a 1.4.x client to mount a1.6.x file system?

[Brian J. Murrell]

On Tue, 2007-12-11 at 10:37 -0800, Rei Lee wrote:
> 
> However, when I  added another OSTs to the upgraded file system,
> only 1.6 clients saw the size increase and file copy worked fine on
> the 1.6 clients .  The file system size did not increase on the 1.4
> clients and file copy failed on the 1.4 client (errors like "No such
> device").   

Indeed.  1.4 clients will only work with 1.6 OSTs that were upgraded
from 1.4 OSTs.  Brand new 1.6 OSTs will not work with 1.4 clients.

> It may not be possible to upgrade the 1.4 clients to 1.6 at this
> point.  Would there be other ways to allow cross mount between
> 1.4 and 1.6 while we are still able to add storage to the 1.6 file
> system?

In theory (meaning this has not been tested and is not advocated -- and
perhaps somebody will tell me I'm wrong), you could create the new OSTs
as 1.4 OSTs by rolling your MDT back to 1.4 and using lconf --write-conf
to write an updated XML configuration and then upgrade the MDT back to
1.6 and then upgrade the new OSTs to 1.6.  Sounds like quite a hassle to
me though.  Personally I'd explore options to get the clients upgraded.

b.