How to emulate GC impact with FEMU

[yanbozyb]

Hi Huaicheng,

When I try FEMU Black box SSD, the write throughput is always around 1180MB/s.

I use default FEMU configuration and FIO tool to measure raw block device. Although I change fio configuration to sequential writes (128KB) and random writes (4KB) multiple times, the throughput remain same (1180MB/s). And I when continue to randomly write entire device, I didn't see any performance degradation as real NAND SSDs.

I'm wondering how can I reproduce GC influence with FEMU? The Black box SSD is expected to show lower write throughput when GC is triggered.

Thanks

[huaicheng]

Try enabling FEMU logs, did you observe GC being triggered?

[yanbozyb]

Thanks for your help.

When I enable FEMU debug log, I find GC is indeed triggered. It seems like GC has visible influence on tail latency, but it hasn't too much visible influence on throughput (around 1-2% throughput degradation for writes).