NDMP backups of Celerra file shares

[LargeMammal]

I have a number of file shares on a Celerra NS502 being backed up with
NDMP to my Legato server. The Celerra is set up as a storage node with
two dedicated tape drives in an Adic Scalar 500 tape library.
Currently, it is taking over a day to complete the backups of the
shares if they ever complete. Some of the shares are 2 TB and larger.
I have been looking to try using the SNAPSURE=Y option to try using a
checkpoint for the backup rather than the actual share. Problem is
that I cannot find anywhere in documentation how to tell the Celerra
which file system I want to use for the automatic checkpoint. I also
need some idea of how much space the checkpoints are going to take. I
have a 2TB file system available for use, which may or may not be
enough. Looking through several white papers, it should be enough to
start, but I am not sure having never used this set of features. Is
anyone using this set up or used it in the past? Also, any other
suggestions from anyone to speed up backups in this situation? Thanks
for any help.
David