The /proc/diskstats file displays the I/O statistics
of block devices. Each line contains the following 14
fields:

==  ===================================
 1  major number
 2  minor mumber
 3  device name
 4  reads completed successfully
 5  reads merged
 6  sectors read
 7  time spent reading (ms)
 8  writes completed
 9  writes merged
10  sectors written
11  time spent writing (ms)
12  I/Os currently in progress
13  time spent doing I/Os (ms)
14  weighted time spent doing I/Os (ms)
==  ===================================

Kernel 4.18+ appends four more fields for discard
tracking putting the total at 18:

==  ===================================
15  discards completed successfully
16  discards merged
17  sectors discarded
18  time spent discarding
==  ===================================

Kernel 5.5+ appends two more fields for flush requests:

==  =====================================
19  flush requests completed successfully
20  time spent flushing
==  =====================================