Setting Up Disk Arrays
Truth be told, most users aren't going to use their NAS too far beyond the actual NAS part, holding data. Synology sells systems with and without drives. Systems sold with drives come preconfigured in what Synology calls SHR or Synology Hybrid RAID. Essentially this is RAID 5, but easier to upgrade to larger drives when needed.
Systems sold without drives will need to be configured. During the initial setup procedure users are presented the option of checking a box for SHR. If you want to use RAID 6 or another array type you need to configure that in the Storage Manager area.
Once you are past the regular disk setup portion you can take the next step and start configuring iSCSI. I've yet to hear of a home user setting up iSCSI targets, but in small offices on up, iSCSI is almost necessity these days.
Synology makes the iSCSI easy for users.