ReadyNAS Ultra 2 RNDU2000 queries (Mac and PC)

I can answer a few of your questions:
1. The system comes with it's own OS, an application called RAIDiator, current version is 4.2.19. The OS is stored on flash memory in the unit and during the setup, it is installed on the drives. Since it is stored on flash memory, it is also referred to in many posts as "firmware". Note: No ReadyNAS will boot without at least one drive installed.

2. It is NOT recommended that you swap disks like that. The SATA connectors on these drives were not designed for frequent plugging and unplugging. The plastic cover over the connectors can be fragile (I have broken two, thus killing the drives). It is also possible to kill a drive with static electricity by handling the drive with the electronics exposed. For routine/regular backups an external HD is recommended. The best way, albeit more expensive, is NAS to NAS backups. It took me several years, but I finally got in that position. You probably need to decide if the Mac files are to be stored on the Mac or the NAS. If they are not Mac specific format files, you may want to store them on the NAS.

2a) The drives will actually be formatted in Ext4, but part of the services is deciding on the file transfer format - CIFS is used for PC's and is transparent to Windows, AFP is used for Macs. The files can co-exist within the same share/folder this way. The level 1 directory/folder in a ReadyNAS is a share and must be set up via Frontview. The unit comes with backup and media shares by default. Sub-folders/sub-directories can be set up by any PC (Windows or Mac) that has access.

3. The unit has a share called backup.

4. The Ultra 2 can be used as a media server. Transcoding a file from one format to another would stress the CPU. If you wanted to do HD it may take an Ultra 2 Plus.

5. I do not know the answer to this one, others may.

I have a concern in that even with 3TB drives, you may outrun the available space if you are storing a great deal of video. Video, especially HD, eats disk space at an alarming rate. The 2 bay unit with redundancy, has the effective storage space of a single drive. A four bay unit (Ultra 4 for example) has the capacity of three times a single disks storage space (again the space of one drive is used for redundancy). An Ultra 2 with redundancy has currently a maximum of 2.7TB storage (net after overhead) and the Ultra 4 has a net storage space of 9.1TB (net after overhead). This is calculated used 3TB drives. Of course when 4TB drives are released and affordable, these maximum storage volumes will increase.

Do not confuse the redundancy for backup. Redundancy allows you to survive the failure of a single drive. It does not protect you against any problems with the unit, or a disaster such as fire, tornado, theft, etc. You will still need a true backup plan. I started several years ago with two 500GB drives in an NV+, which was enough for about 80GB of data that I had at the time. It was easy to backup 80GB to an external drive. As I used the system more, my volume grew until I had expanded to 1.3TB net storage and then increased the drives to 1TB giving me 2.7TB of space. I then added a second NAS so my backups are now NAS to NAS, with external USB drives used for important/critical data backup in addition and then stored off site.

Hope this helps.