4 ms·
Generally, in terms of transfer speed, NVMe is damn close. The latencies is where that hits you because NVMe hasn't nearly as short latencies and doesn't have l
by zaarn 5y ago
Generally, in terms of transfer speed, NVMe is damn close. The latencies is where that hits you because NVMe hasn't nearly as short latencies and doesn't have latency guarantees about the 99th percentile.
If your ops aren't latency sensitive, then NVMe might as well be RAM, if they are latency sensitive, then NVMe is not RAM (yet)
- koala_man 5y agoIsn't it about ~2GB/s vs ~20GB/s? It's really impressive but still an order of magnitude.
- zaarn 5y agoA modern NVMe on PCIe 4.0 can deliver up to 5GB/s, which is only 4 times slower. You can get faster by using RAIDs and I believe some enterprise class stuff can get a bit faster still at the expense of disk space. PCIe 4.0 would top out at 8GB/s, so for faster you'll need PCIe 5.0 (soon).
- nh2 5y agoRAM bandwidth scales with the number of DIMMs used, e.g. a current AMD EPYC machines can do 220 GB/s with 16 DIMMs per spec sheet. How well does NVMe scale to multiple devices, that is, how many GB/s can you practically get today out of a server packed with NVMe until you hit a bottleneck (e.g. running out of PCIe lanes)?
- zaarn 5y agoAn AMD Epyc can have 128 PCIe 4.0 lanes, each 8GB/s, meaning it tops out at a measely 1TB/s of total bandwidth. And you can in fact saturate that with the bigger Epycs. However, You will probably loose 4 lanes to your chipset and local disk setup, maybe some more depending on server setup but it'll remain close to 1TB/s.