fio: add iostat and keep the output files

[Vicente-Cheng]

• that we can do more investigation with these output files

For example, we will get the output like the following.

harvester-node-2:~ # ls output/
Local-Path-bandwidth-iostat.log  Local-Path-iops.json           Local-Path_vs_Longhorn.summary  Longhorn-iops-iostat.log     Longhorn-latency.json
Local-Path-bandwidth.json        Local-Path-latency-iostat.log  Longhorn-bandwidth-iostat.log   Longhorn-iops.json
Local-Path-iops-iostat.log       Local-Path-latency.json        Longhorn-bandwidth.json         Longhorn-latency-iostat.log

We could compare iostat data between Local-Path and Longhorn for further investigation.

[yasker]

Why do we need iostat here? FIO already has the categorized results.

And it's not a good idea to bind mount a host directory just to copy the files out, since the privilege would need to be escalated.

[Vicente-Cheng]

Hi @yasker, thanks for the review.
We need the iostat data because we could do further investigation.
Sometimes, the performance issue will related to the physical device.
Through the device queue length, request size, wait time ... etc. We can get more info to figure out the performance issue.

[yasker]

I see. A few comments here:

1. Is there a way for us to figure out the block device without specifying it manually?
2. Does it work if we pass in the block devices directly (see volumeDevices section)?
3. Can we find another way to get those outputs without requiring an elevated privilege?