Common pitfall when benchmarking ZFS with fio

Paul Witek — Wed, 26 Jan 2022 22:23:20 GMT

Let's say you build yourself a new ZFS pool on top of some pretty fast NVMe drives and want to benchmark it to see how well it can run. You create a zvol and fire up fio to sequentially read some data from it. But anticipating a large number of IOPS, you don't want your CPU to bottleneck the performance, so naturally you include --numjobs=8 to be sure you get the most out of your NAND gates. Fio completes and TA-DAH: IOPS up the roof. But wait a minute... Your pool consisting of three NVMe drives, each capable of 3.2 GB/s sequential read, is read at the rate of 24 GB/s! Obviously the disk vendor would not undermine its product perfromance, so something might be wrong with the test.

pV-tech (Posts about zfs)

Common pitfall when benchmarking ZFS with fio