Tuesday, May 6, 2008

Hidden switch: Display disk total statistics including time spent reading and writing data

Most Linux admins are not aware of vmstat's hidden switch (undocumented switch) called -D, which 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 -D
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 a backup server hosted at data center:
$ uptime
12:15:07 up 33 days, 9:15, 2 users, load average: 1.71, 1.49, 1.03

Since last 33 days the server spent total 1180260353 milliseconds reading disk. To get more detailed about disk I/O stats, use the -d option

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