iSCSI random read

In Figure 1 a random-read FIO workload is running against a file system using iSCSI-connected devices. The workload is scaled from 1 to 128 jobs running on the KVM guest. The V7000 storage devices are directly attached to the KVM host system via iSCSI.

iSCSI throughput measurement peaks at 16 jobs and stays constant for 32 jobs. CPU load on the KVM host reaches a peak of 2.5 CPUs at 32 jobs. Reviewing data collected during the runs, it was observed that I/O service-time increases by a factor of 7 between 32 and 64 jobs, mirroring the fall off of throughput starting at 64 jobs.