Disk Throughput

What this shows

The graph below shows measured sustained data transfer rate of one disk drive in Mbytes per second. It is intended as a baseline for comparison purposes.

disk_throughput.png

How generated

The image was generated during a run of badblocks on a SATA drive while running the command iostat -k 60. As such each figure obtained and each point on the graph is a 60-second average. It thus measures the rate of transfer to or from the hard disk platters rather than the faster performance that would be obtained by short reads or writes of the disk internal cache.

Interpretation

The peak of each curve can be interpreted to be the rate at the outside of the disk at 78Mby/s. The rate reduces over time to 38Mby/s on inner cylinders. The read and write rates are similar so if you want to conduct a similar test reading the disk is sufficient, as shown next.

Taking measurements

To take similar measurements on a Unix-family system use the following guidelines. They show sdb as an example disk drive and are designed to show disk read speed and not write to the disk being tested. However, you should check your local documentation for each command to ensure you are using the right (i.e. non destructive) command and switches for your system.

Ensure you are not intending to test a disk which is being used for swapping.

cat /etc/fstab | grep swap

If not a swap disk find the mounted partitions with

df | grep sdb

Unmount any mounted partitions with

umount /dev/sdb1
umount /dev/sdb5
etc.

Set up comparative monitoring in one command shell window

iostat -k 60 | grep /dev/sdb
This will return 60-second averages for comparison with the graph above. For additional information you may want to run a shorter-duration report in another window such as
iostat -k 3 | grep /dev/sdb

Finally, in another window use badblocks in read-only mode (check your own system's documentation to be sure you use a read-only test) such as

badblocks /dev/sdb

Once done remount the partitions.

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