I don't see anything that's not expected from the process/syslogs.
At the time of the diagnostics capture it shows you have 2 "rsync" processing running that's causing the load from the "unbalance" plugin.
nobody 15606 0.4 0.1 110180 14136 ? Sl 11:04 0:18 /usr/local/emhttp/plugins/unbalance/unbalance -port 6237
nobody 27569 21.4 0.0 20164 3308 ? D 12:03 0:39 \_ /usr/bin/rsync -avPR -X Video/Action Cam /mnt/disk2/
nobody 27570 0.0 0.0 19556 2556 ? S 12:03 0:00 \_ /usr/bin/rsync -avPR -X Video/Action Cam /mnt/disk2/
nobody 27571 15.3 0.0 19996 2384 ? S 12:03 0:28 \_ /usr/bin/rsync -avPR -X Video/Action Cam /mnt/disk2/
From your SMARTS on your cache drive(s), I'm not sure if the RAW value has any meaning for SSDs, but for most spinners, it does for field 187. Do you have a lot of power outages? If not, perhaps your power plane for the cache drives needs to be corrected. The larger ones report a number of "unexpected power loss" as well.
Model Family: SandForce Driven SSDs
Device Model: SanDisk SDSSDA240G
Serial Number: 154836404031
LU WWN Device Id: 5 001b44 f188d033f
Firmware Version: Z22000RL
User Capacity: 240,057,409,536 bytes [240 GB]
174 Unexpect_Power_Loss_Ct -O--CK 100 100 000 - 24
187 Reported_Uncorrect -O--CK 100 100 000 - 5872
0x04 0x008 4 5872 --- Number of Reported Uncorrectable Errors
---
Model Family: SandForce Driven SSDs
Device Model: SanDisk SDSSDA240G
Serial Number: 161337404732
LU WWN Device Id: 5 001b44 4a4758b33
Firmware Version: Z22000RL
User Capacity: 240,057,409,536 bytes [240 GB]
174 Unexpect_Power_Loss_Ct -O--CK 100 100 000 - 16
187 Reported_Uncorrect -O--CK 100 100 000 - 2
0x000a 2 4 Device-to-host register FISes sent due to a COMRESET
SMART Extended Comprehensive Error Log Version: 1 (1 sectors)
Device Error Count: 1
CR = Command Register
FEATR = Features Register
COUNT = Count (was: Sector Count) Register
LBA_48 = Upper bytes of LBA High/Mid/Low Registers ] ATA-8
LH = LBA High (was: Cylinder High) Register ] LBA
LM = LBA Mid (was: Cylinder Low) Register ] Register
LL = LBA Low (was: Sector Number) Register ]
DV = Device (was: Device/Head) Register
DC = Device Control Register
ER = Error register
ST = Status register
Powered_Up_Time is measured from power on, and printed as
DDd+hh:mm:SS.sss where DD=days, hh=hours, mm=minutes,
SS=sec, and sss=millisec. It "wraps" after 49.710 days.
Error 1 [0] log entry is empty
SMART Extended Self-test Log Version: 1 (1 sectors)
No self-tests have been logged. [To run self-tests, use: smartctl -t]
---
Model Family: SandForce Driven SSDs
Device Model: TS64GSSD320
Serial Number: A2910611949538650037
LU WWN Device Id: 0 0232d0 000000000
Firmware Version: 5.0.2
User Capacity: 64,023,257,088 bytes [64.0 GB]
174 Unexpect_Power_Loss_Ct ----CK 000 000 000 - 122
0x0009 2 1 Transition from drive PhyRdy to drive PhyNRdy
0x000a 2 1 Device-to-host register FISes sent due to a COMRESET