Storage FW 8.3.1.2+: Monitor

Since that storage firmware Monitor role can be used.

Storage FW 8+: RestrictedAdmin

Role RestrictedAdmin must be used.
Role desciption as per manual: Users can complete the same tasks and run most of the same commands as administrator-role users. However, users with the Restricted Administrator role are not authorized to run the rmvdisk, rmvdiskhostmap, rmhost, or rmmdiskgrp commands

Storage FW 7 and older: Administrator

Why do we need "Administrator" role here?

The problem is that one command which is necessary for downloading of statistical data requires Administrator role.
It is command: svctask cpdumps
The cpdumps command copies dump files from a nonconfiguration node onto the configuration node.
Data can be retrieved via scp only from the configuration node.
The problem is same for getting of data through CIMOM or TPC.