43 ms·
> Sequential spinny disk access is faster than SSD random access. No it’s not. At least not with modern SSDs or NVMe storage. Even at 100 MB/s, a spinning dis
by koolba 4y ago
> Sequential spinny disk access is faster than SSD random access.
No it’s not. At least not with modern SSDs or NVMe storage.
Even at 100 MB/s, a spinning disk in sequential mode is doing 100 x 1024 / 4 = 25,600 IOPS (assuming a standard 4K per operation).
Even consumer grade NVMe hardware gets 5-10x of that for random workloads.
- deleted 4y ago[deleted]
- kragen 4y agoit is true that spinning rust is slower than most ssds including nvme ssds even in sequential mode however, a spinning disk doing a sequential access is not doing 25600 iops if the sequential access lasts 10 seconds it is doing 0.1 iops
- mrkeen 4y ago> Even consumer grade NVMe hardware gets 5-10x of that for random workloads. Cool, lots of IOPS! But like I said, I got it down to kilobytes/sec.
- koolba 4y agoOn what hardware and how much parallelization? The max IOPS numbers are only when you’re saturating the command queue. It’s a throughput number, not a single operation, completion, followed by the next one.
- justsomehnguy 4y agoBecause you did it the most inefficient way. This [0] comment is totally on point. Also note what a consumer SSDs can be made even with a single flash chip. A more performant ones are made of bunch of chips internally (essentially a RAID0 with some magic) so they can do a parallel operations if the data resides on the different flash blocks. Still, if your thread is only doing one operation a time with blocks < flash rewrite block size you will hit the write amplification anyway. I think if you do the same test but without a memory mapped file (ie let the OS and disk subsystem do their thing) you will get much more speed. [0] https://news.ycombinator.com/item?id=33751973 https://news.ycombinator.com/item?id=33751973