about Veritas Access Appliance

1). can an Access Appliance be configured on existing media server as storage pool, run SLP from MSDP to it? 

You configure the Access Appliance as a new media server, with its own disk pool, and duplicate data from MSDP to the Access Appliance (recommended method), or you can back up directly to the Access Appliance.

2). Is the data in Access Appliance deduplicated ? Will any additional DDPO license be needed for Access Appliance. I heard the OpenDedu is being used on Access Appliance.

Unsure about the licensing part, but the data in Access is deduplicated. The recommended configuration is to have the deduplication occur on the MSDP media server, then duplicate that data to the Access Appliance for LTR, but Access has a deduplication engine and can dedupe data sent directly to it. As Riann pointed out, the Access Appliance can be a replication target for other domains, and allows for global dedupe.

3). Can the Access Appliance be shared by multiple media servers?

Yes, it can be shared among one or many media servers.

4). Can the access appliance be used as CIFS/NAS servers?

The Access Appliance is a NAS server, and it can be configured as a CIFS server. See this section of the Access Admin guide for more info on CIFS shares: https://www.veritas.com/content/support/en_US/doc/125480392-133637289-0/uxrt-tot_v125453943-133637289

5). Is there any way to test out before purchase?  

Speak to your Veritas account rep for info on pre-purchase trials.