We also have just purchased a NS20 to consolidate disk storage. We also have a EMC DL210 for disk-to-disk backup. With NDMP enabled and the Agent License loaded on Backup Exec, I cannot backup anything other than the NS20 to the DL210. Backup Exec will log an error when defining a new job for another resource on the network that states you cannot backup a non NDMP resource to a NDMP resource. In talking to EMC about how other customers configure backup for the NS20, they stated that they have disk-to-disk directly attached(or zoned - fibre channel) to the NS20 and then a tape drive attached to the disk-to-disk to write off to tape. My understanding of using NDMP is Backup Exec is requesting the NS20 to back itself up instead of the backup server performing the backup.
Our original configuration has 2 backup servers with 2 hbas each zoned to the disk-to-disk and tape library. Everything is backed up over the network to the backup servers and out to the disk-to-disk and then a duplicate job runs that copies from the disk-to-disk to the tape library.
I have just turned off NDMP on the NS20 and will be testing backing up the NS20 over the network. You have to enable selection of user shares under the options tab, networking and security.
A question to you: have you thought about virus protection on the NS20 and if so, what are you using?