Testing local storage device for performance requirements

To achieve the best performance with Native Cloud Object Storage, your local storage device must meet certain requirements. Before you use a local storage device for the caching tier, you must test the device to validate the device's performance.

About this task

The local storage device for the caching tier is a critical component to the performance of the Native Cloud Object Storage (NCOS) support in Db2® Warehouse 11.5.9.

Note: You must follow this testing procedure to validate the local storage device performance on all hosts.

Procedure

To test if your local storage device meets the performance requirements, run this command:
```
dd if=/dev/zero of=/path/on/local/disk/testfile bs=1M count=10000 oflag=direct,dsync
```
While the dd command is running, run the iostat command in another terminal window on the same system to monitor disk performance:
```
iostat -xyz 1
```
You can determine the pertinent data for meeting performance requirements from the iostat output.
To achieve the best performance with NCOS, test your local storage device to confirm that it meets all of these requirements:
- Write throughput is at least 600 MB/s (see value under wkB/s column)
- Write latency is under 20 ms (see value under w_await column)

Example

This iostat output is an example from a device that meets the local storage performance requirements:

Device:         rrqm/s   wrqm/s     r/s      w/s      rkB/s     wkB/s     avgrq-sz avgqu-sz   await   r_await  w_await  svctm  %util
sdc              0.00     0.00      0.00   12555.00    0.00    803520.00   128.00   141.84    11.30     0.00    11.30    0.08  100.00

This successful output shows that the example local storage device has:

Write throughput at 803 MB/s (exceeds 600 MB/s)
Write latency at 11.3 ms (less than 20 ms)

For comparison, this example output is from a device that does not meet the performance requirements:

Device:          rrqm/s   wrqm/s     r/s     w/s      rkB/s     wkB/s      avgrq-sz  avgqu-sz   await   r_await  w_await  svctm  %util
sdc               0.00    20.00      0.00   2786.00    0.00   680715.00     488.67    150.09    53.85     0.00    53.85    0.36  100.00

This unsuccessful output shows that the example local storage device has:

Write throughput at 680 MB/s (exceeds 600 MB/s)
Write latency at 53.85 ms (more than 20 ms)

Though this local storage device has a write throughput that meets the requirements, the write latency is too high.