Default OIO is “2” if no other parameters are specified

This is documented on the diskpsd page but most workload generators that i use will default to a single OIO, so it’s worth pointing out.

Default case:

The -o parameter is per-disk and per thread.

Run diskspd with -o 32 (single thread) generates a total of 32 OIO

Run diskspd with -o 32 and -t2 (two threads) generates a total of 64 OIO

Run diskspd with -o32, -t8 (eight threads) generates a total of 256 OIO

Run diskspd with -o32, -t8 (eight threads) and 4 Disks – generates 1024 total OIO

Threads and OIO are per disk device.

Using the above with 4 disks will yield 1024 OIO more than most physical HBA’s can deliver by default

To keep total OIO constant across disk count use -O and -F

4 Devices

2 Devices

1 Device

Creating a file with -Zr does not fill the file.

To create a file with non-null bytes, you will have to do a separate write phase after initial creation.

The default fill pattern is highly compressible

• Writing out a file without a switch writes a Repeating pattern every 256 bytes. A 1FFF file will compress by KKK% to JJJbytes
• Writing out a file with “-Z” writes NULL bytes
• Writing out a file with “-Zr” writes totally random bytes.

“Raw” devices are supported

diskspd supports writing directly to the drive (e.g. without a filesystem) using the format #<disknum>

Writing to a file/device without a time period will default to 10 seconds

Anyone coming from e.g. fio might expect the write to fill the entire file.