Most Linux admins are not aware of hidden switch (undocumented switch) called -D. The -D option display a nice summery of disk I/O subsystem since boot time. Output includes total time spent reading and writing data, merged reads and merged writes (kernel disk i/o optimization technique) and other parameters.
vmstat command with -D option
Type the command at shell prompt:
30 disks 8 partitions 13739406 total reads 3887474 merged reads 1180260353 read sectors 109630647 milli reading 118650080 writes 250115464 merged writes 2950543038 written sectors 2382220771 milli writing 0 inprogress IO 113832 milli spent IO
This is my local backup server hosted at local data center:
12:15:07 up 33 days, 9:15, 2 users, load average: 1.71, 1.49, 1.03
Since last 33 days my server spent total 1180260353 milliseconds reading disk. To get more detailed about disk I/O stats, use the -d option as described in previous article - How do I find out Linux Disk utilization?