Readynas Duo & Swapping out Disk 1

So I can just take the disk out of slot 1 and replace with new drive. Will the contents of Disk 2 replicate over to Disk 1 for Redundancy?

Here is the SMART+ stats.

Model: ST32000542AS
Serial: 9XW0F323
Firmware: CC34
SMART Attribute
Spin Up Time 0
Start Stop Count 1288
Reallocated Sector Count 2423
Power On Hours 20374
Spin Retry Count 0
Power Cycle Count 1277
Runtime Bad Block 0
End-to-End Error 0
Reported Uncorrect 4
Command Timeout 0
High Fly Writes 1
Airflow Temperature Cel 42
Temperature Celsius 42
Current Pending Sector 682
Offline Uncorrectable 682
UDMA CRC Error Count 0
Head Flying Hours 228754253176284
Total LBAs Written 4012443717
Total LBAs Read 2606630131
ATA Error Count 4

Extended Attribute
Hot-add events 0
Hot-remove events 0
Lp stat events 9
Power glitches 0
Hard disk resets 0
Retries 0
Repaired sectors 0

The main concern is the reallocated sector count and ATA error count.

The SMART+ stats for Disk 2 are as follows. I do see that the Reallocated sector count on this is also 9 - must have just started as perviously this drive was 0.

SMART Information for Disk 2

Model: ST32000542AS
Serial: 9XW0EVFA
Firmware: CC34
SMART Attribute
Spin Up Time 0
Start Stop Count 0
Reallocated Sector Count 9
Power On Hours 20443
Spin Retry Count 0
Power Cycle Count 1278
Runtime Bad Block 0
End-to-End Error 0
Reported Uncorrect 0
Command Timeout 0
High Fly Writes 5
Airflow Temperature Cel 40
Temperature Celsius 40
Current Pending Sector 0
Offline Uncorrectable 0
UDMA CRC Error Count 0
Head Flying Hours 199329432231392
Total LBAs Written 2380022397
Total LBAs Read 975174830
ATA Error Count 0

Extended Attribute
Hot-add events 0
Hot-remove events 0
Lp stat events 0
Power glitches 0
Hard disk resets 0
Retries 0
Repaired sectors 0

Any help would be appreciated.

thanks!
pjcools