RN102 Very Slow Speeds on One HDD

Had a look at this file and it all seems fine. This is the data output from the file. Accessing that second drive is still very slow. And I just can't work it out. Thanks for your replies by the way. Have just found some time to try things out. I've tried downgrading to previous firmware but it didn't seem to make a difference.

Device: sda
Controller: 0
Channel: 0
Model: ST2000DM001-1CH164
Serial: W1E1N58K
Firmware: CC43
Class: SATA
RPM: 7200
Sectors: 3907029168
Pool: Drive1
PoolType: RAID JBOD
PoolState: 2
PoolHostId: e341ff9
Health Data:
ATA Error Count: 0
Reallocated Sectors: 0
Reallocation Events: 0
Spin Retry Count: 0
End-to-End Errors: 0
Command Timeouts: 0
Current Pending Sector Count: 0
Uncorrectable Sector Count: 0
Temperature: 37
Start/Stop Count: 79
Power-On Hours: 7114
Power Cycle Count: 62
Load Cycle Count: 79

Device: sdb
Controller: 0
Channel: 1
Model: ST2000DM001-1E6164
Serial: Z1E28B8S
Firmware: CC42
Class: SATA
RPM: 7200
Sectors: 3907029168
Pool: Drive2
PoolType: RAID JBOD
PoolState: 2
PoolHostId: e341ff9
Health Data:
ATA Error Count: 0
Reallocated Sectors: 0
Reallocation Events: 0
Spin Retry Count: 0
End-to-End Errors: 0
Command Timeouts: 0
Current Pending Sector Count: 0
Uncorrectable Sector Count: 0
Temperature: 37
Start/Stop Count: 59
Power-On Hours: 5000
Power Cycle Count: 59
Load Cycle Count: 59