Sudden inflation in Disk IO operations

Hi,

From last 7 days I am getting sudden spikes in Disk IO Operations. These spikes start happening out of blue and I have 120 plugins installed in my network so I cannot do it by disabling a plugin at a time.

I am using SSD Hard Disk, Google Compute Engine (ns-1-standard-2) and Google Cloud SQL (db-1-standard-1) - 2nd Generation.

I have a MultiSite network with WP All Import Job running from last 1 month. (It will run for 6 more months).

How shall I go about debugging this issue?

rohit@instance-1:~$ sudo iotop
Total DISK READ : 1112.70 K/s | Total DISK WRITE : 31.63 K/s
Actual DISK READ: 1302.46 K/s | Actual DISK WRITE: 16.18 M/s
TID PRIO USER DISK READ DISK WRITE SWAPIN IO> COMMAND
11064 be/4 daemon 23.00 K/s 0.00 B/s 0.00 % 99.99 % php-fpm: pool wordpress
32 be/4 root 0.00 B/s 0.00 B/s 0.00 % 99.99 % [kswapd0]
10893 be/4 daemon 0.00 B/s 0.00 B/s 0.00 % 93.71 % php-fpm: pool wordpress
7792 be/4 daemon 8.63 K/s 0.00 B/s 9.25 % 92.60 % php-fpm: pool wordpress
7802 be/4 daemon 5.75 K/s 0.00 B/s 9.47 % 91.27 % php-fpm: pool wordpress
10669 be/4 daemon 14.38 K/s 0.00 B/s 0.00 % 75.43 % php-fpm: pool wordpress

sudo iotop
Total DISK READ : 5.28 M/s | Total DISK WRITE : 0.00 B/s
Actual DISK READ: 5.34 M/s | Actual DISK WRITE: 8.83 M/s
TID PRIO USER DISK READ DISK WRITE SWAPIN IO> COMMAND
11064 be/4 daemon 1484.92 K/s 0.00 B/s 0.00 % 99.99 % php-fpm: pool wordpress
11108 be/4 daemon 469.26 K/s 0.00 B/s 3.81 % 92.39 % php-fpm: pool wordpress
11065 be/4 daemon 138.21 K/s 0.00 B/s 7.84 % 85.48 % php-fpm: pool wordpress
11301 be/4 daemon 3.21 K/s 0.00 B/s 0.00 % 77.98 % php-fpm: pool wordpress
7147 be/4 daemon 77.14 K/s 0.00 B/s 18.60 % 75.01 % php-fpm: pool wordpress
10895 be/4 daemon 257.13 K/s 0.00 B/s 0.00 % 59.88 % php-fpm: pool wordpress
32 be/4 root 0.00 B/s 0.00 B/s 0.00 % 58.07 % [kswapd0]
11265 be/4 daemon 212.13 K/s 0.00 B/s 42.00 % 4.08 % php-fpm: pool wordpress
11315 be/4 root 102.85 K/s 0.00 B/s 0.00 % 1.55 % python /usr/sbin/iotop
10667 be/4 daemon 224.99 K/s 0.00 B/s 99.99 % 0.00 % php-fpm: pool wordpress
10669 be/4 daemon 228.20 K/s 0.00 B/s 99.99 % 0.00 % php-fpm: pool wordpress
10894 be/4 daemon 224.99 K/s 0.00 B/s 99.99 % 0.00 % php-fpm: pool wordpress
11060 be/4 daemon 199.28 K/s 0.00 B/s 99.99 % 0.00 % php-fpm: pool wordpress
11063 be/4 daemon 231.42 K/s 0.00 B/s 99.99 % 0.00 % php-fpm: pool wordpress
9064 be/4 daemon 22.50 K/s 0.00 B/s 10.03 % 0.00 % httpd.bin -f /opt/bitnami/ap~f/httpd.conf -DDISABLE_BANNER
11141 be/4 daemon 228.20 K/s 0.00 B/s 99.99 % 0.00 % php-fpm: pool wordpress
11158 be/4 daemon 228.20 K/s 0.00 B/s 99.99 % 0.00 % php-fpm: pool wordpress
11196 be/4 daemon 57.85 K/s 0.00 B/s 64.21 % 0.00 % php-fpm: pool wordpress
7144 be/4 daemon 192.85 K/s 0.00 B/s 99.99 % 0.00 % php-fpm: pool wordpress
11267 be/4 daemon 231.42 K/s 0.00 B/s 99.99 % 0.00 % php-fpm: pool wordpress
7802 be/4 daemon 51.43 K/s 0.00 B/s 49.83 % 0.00 % php-fpm: pool wordpress
7792 be/4 daemon 83.57 K/s 0.00 B/s 63.64 % 0.00 % php-fpm: pool wordpress
7803 be/4 daemon 224.99 K/s 0.00 B/s 99.99 % 0.00 % php-fpm: pool wordpress
10896 be/4 daemon 228.20 K/s 0.00 B/s 99.99 % 0.00 % php-fpm: pool wordpress

I receive only 5000 visits in a month so very less load.