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Testing Disk I/O Performance in Linux


Notes for testing I/O on Linux after moving into a new VPS.

Testing write speed:
# dd if=/dev/zero of=/tmp/test1.img bs=1G count=1 oflag=dsync

bs=1G	(Block Size - Sets the size of write test).
count=1	(Count - Number of blocks you want to write).
oflag=dsync	(Synchronized I/O to prevent cached results).

Writing a single big block of data will challenge pure write performance.

Testing disk latency:
# dd if=/dev/zero of=/tmp/test2.img bs=512 count=1000 oflag=dsync

if	(input.file - Where to read data from).
of	(output.file - Where to write data to).
bs=512	(Block Size - Sets the size of write test).
count=1000	(Count - Number of blocks you want to write).
oflag=dsync	(Synchronized I/O to prevent cached results).

Writing small blocks 1000 times will challenge latency and reaction time.

Testing read speed(s):
# hdparm -Tt /dev/vda1

-T	(Perform cache read timings).
-t	(Perform device read timings).


Results (respectively):


Write:
1073741824 bytes (1.1 GB) copied(1 time), 0.954025 s, 1.1 GB/s

Latency:
512000 bytes (512 kB) copied(1000 times), 4.88921 s, 105 kB/s

Read:
Timing cached reads: 31032 MB in 2.00 seconds = 15535.43 MB/sec
Timing buffered disk reads: 1754 MB in 3.00 seconds = 584.23 MB/sec