Home > Storage > PowerScale (Isilon) > Industry Solutions and Verticals > Electronic Design Automation > PowerScale: Best Practices for Semiconductor EDA Design Environments > Direct Read and Direct Write
For streaming reads from low-latency SSD media, the cache benefit of prefetching is typically less than the overhead. To address this benefit, OneFS 9.5 and later releases automatically disable L2 cache prefetching for concurrent and streaming reads from SSD media, in a process known as Direct Read. However, L2 caching is still used when prefetching data blocks from spinning disk (HDD).
Similarly, OneFS 9.7 introduces Direct Write, also known as NCIO or non-cached I/O, which is a feature that targets the NVMe-based F series platforms and operates by bypassing cache to increase write throughput.
Writes to newly allocated blocks are identified and queued directly to the drives, by skipping the L2 cache and journal. This allows OneFS to better utilize the NVMe drives, reducing I/O access latency, and freeing up L2 cache and journal bandwidth for writes. And this will help in any streaming write or heavy sequential write workload.
Direct Write is analogous to the L2-bypass Direct Read functionality described above. Enabled by default in 9.7, it requires no license, is not user configurable, and, as such, has no CLI or WebUI interface.
Direct Read – see above description.
Direct Write is enabled by default on OneFS 9.7 and above.
EDA workloads can benefit from both Direct Read and Direct Write to reduce I/O access latency on all-flash F series platforms.
Note: OneFS 9.5 and above introduces Direct Read. OneFS 9.7 introduces Direct Write. For all-flash F series platforms.
For high capacity NVMe QLC drive, write speed is slower than high speed NVMe TLC drive. Consider turn off Direct Write to improve write performance and latency.
For high speed NVMe TLC drive, recommended to use Direct Write to improve write performance and latency.
To disable Direct Write for high capacity NVMe QLC drive only, use below command.
# isi_sysctl_cluster efs.lbm.ncio.write.enable=0