Demonstrations of disksnoop.py, the Linux eBPF/bcc version.

This traces block I/O, a prints a line to summarize each I/O completed:

# ./disksnoop.py

TIME(s) T BYTES LAT(ms)

16458043.435457 W 4096 2.73

16458043.435981 W 4096 3.24

16458043.436012 W 4096 3.13

16458043.437326 W 4096 4.44

16458044.126545 R 4096 42.82

16458044.129872 R 4096 3.24

16458044.130705 R 4096 0.73

16458044.142813 R 4096 12.01

16458044.147302 R 4096 4.33

16458044.148117 R 4096 0.71

16458044.148950 R 4096 0.70

16458044.164332 R 4096 15.29

16458044.168003 R 4096 3.58

16458044.171676 R 4096 3.59

16458044.172453 R 4096 0.72

16458044.173213 R 4096 0.71

16458044.173989 R 4096 0.72

16458044.174739 R 4096 0.70

16458044.190334 R 4096 15.52

16458044.196608 R 4096 6.17

16458044.203091 R 4096 6.35

The output includes a basic timestamp (in seconds), the type of I/O (W == write,

R == read, M == metadata), the size of the I/O in bytes, and the latency (or

duration) of the I/O in milliseconds.

The latency is measured from I/O request to the device, to the device

completion. This excludes latency spent queued in the OS.

Most of the I/O in this example were 0.7 and 4 milliseconds in duration. There

was an outlier of 42.82 milliseconds, a read which followed many writes (the

high latency may have been caused by the writes still being serviced on the

storage device).