Ready for expansion (RN Pro Pioneer Edition)-Seeking Advice

winger13 wrote:
ATA error: The SATA controller on the ReadyNAS was unable to communicate with the hard drive. Does this (ATA error) mean a portion of the disk could not be read?

No. It is more basic than that. The ReadyNAS and the disks communicate over the SATA interface, using ATA commands. An ATA error means that communication failed. An ATA command could have been garbled somehow (due to a problem in the NAS controller, the SATA backplane or the drive controller). Or the drive might be returning an error for some other reason. It could be related to a disk read/write error, but often isn't.

What happens when that failure occurs depends on the command, and what the NAS (and drive) do when they detect an error. It is not possible to give a general answer. Though I haven't seen data loss on my systems due to ATA errors.

winger13 wrote:
And scrubbing ensures all my data is intact across all my six disks, even if this involves "moving" data from the portion of the disk not readable to another location (NAS knows what this 'unreadable' data based on my dual-redundancy setup.

Close enough probably. It verifies that all the data can be read, and it will reconstruct blocks that it cannot read from the dual-redundancy setup. As I tried to say above, there are cases where it doesn't help, and some where it can actually make things worse. Although those cases are rare, it does make me cautious about running a scrub when I have suspect disks. That was why I wanted to see the SMART stats first.

I agree with mdgm that you should run both the on-line file system check, and the scrub periodically. And maintain at least one backup on another device.