Ubuntu on Dell Lattitude E5550 slows down

I have installed Ubuntu 18.04.3 LTS on my laptop. The specs are:

Corei7
16 GB RAM
Seagate Firecuda 1 TB HDD ST1000LX015-1U71

The main partition is EXT4, and my home partition is ZFS

The system gets very slow at times (not always). The HDD light is on continously, but there is not much activity going on. Sync takes sometimes 7-8 mins to complete, the load average jumps to 10 or above and the io-wait goes to above 50%. The harddisk is brand new (just 11 days and 19 hours power on time).

The data I have collected is:

    #time sync

    real    3m37.626s
    user    0m0.001s
    sys 0m0.010s

    #top
    top - 10:00:03 up 1 day,  1:32,  1 user,  load average: 11.52, 12.43, 8.58
    Tasks: 420 total,   1 running, 363 sleeping,   0 stopped,   0 zombie
    %Cpu(s):  6.6 us,  1.7 sy,  0.0 ni, 20.9 id, 70.8 wa,  0.0 hi,  0.2 si,  0.0 st
    KiB Mem : 16267860 total,  1294616 free, 11784256 used,  3188988 buff/cache
    KiB Swap: 15625212 total, 15403572 free,   221640 used.  2891476 avail Mem 

    #iostat -t 1 | grep sda
    Device             tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn
    sda              16.18       100.05       364.08    9185989   33429161
    sda              10.00       224.00         0.00        224          0
    sda               0.00         0.00         0.00          0          0
    sda              29.00       952.00      2508.00        952       2508
    sda               7.00       292.00         0.00        292          0
    sda               0.00         0.00         0.00          0          0
    sda              41.00      1684.00      1072.00       1684       1072
    sda               0.00         0.00         0.00          0          0
    sda               3.00       264.00         0.00        264          0
    sda              18.00       896.00        36.00        896         36

    #iotop
    Total DISK READ :     147.96 K/s | Total DISK WRITE :       6.64 K/s
    Actual DISK READ:     101.55 K/s | Actual DISK WRITE:     734.63 K/s
      TID  PRIO  USER     DISK READ  DISK WRITE  SWAPIN     IO>    COMMAND                                                                                                       
      303 be/3 root        0.00 B/s    3.97 K/s  0.00 % 99.90 % [jbd2/sda2-8]
      968 be/0 root        0.00 B/s    0.00 B/s  0.00 % 35.63 % [z_wr_iss]
      969 be/0 root        0.00 B/s    0.00 B/s  0.00 % 35.63 % [z_wr_iss]
      970 be/0 root        0.00 B/s    0.00 B/s  0.00 % 35.63 % [z_wr_iss]
      972 be/0 root        0.00 B/s    0.00 B/s  0.00 % 17.77 % [z_wr_int]
     7077 be/4 libvirt-   13.49 K/s  406.19 B/s  0.00 % 17.73 % qemu-system-x86_64 -enable-kvm -name guest=win7-1,debug-~d=balloon0,bus=pci.0,addr=0x8 -msg timestamp=on [worker]
     7245 be/4 libvirt-   13.49 K/s    0.00 B/s  0.00 % 15.31 % qemu-system-x86_64 -enable-kvm -name guest=win7-1,debug-~d=balloon0,bus=pci.0,addr=0x8 -msg timestamp=on [worker]
     7247 be/4 libvirt-   13.49 K/s    0.00 B/s  0.00 % 15.29 % qemu-system-x86_64 -enable-kvm -name guest=win7-1,debug-~d=balloon0,bus=pci.0,addr=0x8 -msg timestamp=on [worker]
     7251 be/4 libvirt-  812.38 B/s 1117.03 B/s  0.00 % 14.29 % qemu-system-x86_64 -enable-kvm -name guest=win7-1,debug-~d=balloon0,bus=pci.0,addr=0x8 -msg timestamp=on [worker]
     7069 be/4 libvirt-   13.49 K/s    0.00 B/s  0.00 % 14.14 % qemu-system-x86_64 -enable-kvm -name guest=win7-1,debug-~d=balloon0,bus=pci.0,addr=0x8 -msg timestamp=on [worker]
      971 be/0 root        0.00 B/s    0.00 B/s  0.00 %  3.07 % [z_wr_iss_h]

It seems that the storage is very slow thus even small data transfers takes a long time, but I am not sure how to confirm which hardware component is faulty. Please help.