3 ms·

Note that the numbers presented in that review are for single-threaded benchmarks, when the current best practices for a server application that really has a lo

Note that the numbers presented in that review are for single-threaded benchmarks, when the current best practices for a server application that really has a lot of write traffic would be to split the work over multiple threads, and preferably use io_uring for both network and disk IO. Even on those consumer-grade SSDs, that would allow for much higher throughput than what's presented in that review—though most of those consumer-grade SSDs wouldn't be able to sustain such write performance for very long. Right now, a lot of software that wasn't written specifically with SSDs in mind is effectively bottlenecked on the CPU side with system call overhead, or is limited by the SSD's latency while using only a fraction of its potential throughput because the drive is only given one or a few requests to work on at a time. If you do write your software with fast storage in mind, and have the fastest SSD money can't quite buy, the results can be very different: https://lore.kernel.org/io-uring/4af91b50-4a9c-8a16-9470-a51430bd7733@kernel.dk/T/#u https://lore.kernel.org/io-uring/4af91b50-4a9c-8a16-9470-a51...

Rafuino 6y ago
Wow, the author himself! Thanks for the great details. I missed the detail in the article about single threaded testing, so thanks for clarifying. I definitely see the specs for the Samsung drive show higher peak random IOPS but I'm always trying to look past the marketing hype and see what's more realistic. What allows an enterprise-grade SSD to sustain writes longer than a consumer-grade SSD? I assume it's cache related (SLC or DRAM), but I'm still learning. Awesome results from Jens there...
- wtallis 6y ago
  Enterprise SSDs often (but not always) reserve more spare area out of the pool of flash on the drive, which helps a lot with sustained write speeds, especially random writes; the garbage collector is under less pressure to free up erase blocks for new writes. Consumer SSDs use SLC caching which allows for much higher write speeds until that cache runs out, but then the drive is stuck with the job of cleaning up that cache while also still handling new writes. So for the same amount of raw NAND capacity and same usable capacity, an enterprise drive that doesn't do any SLC caching at all will tend to have a better long-term write speed than the post-cache write speed on a consumer drive.

Rafuino 6y ago

Wow, the author himself! Thanks for the great details. I missed the detail in the article about single threaded testing, so thanks for clarifying. I definitely see the specs for the Samsung drive show higher peak random IOPS but I'm always trying to look past the marketing hype and see what's more realistic. What allows an enterprise-grade SSD to sustain writes longer than a consumer-grade SSD? I assume it's cache related (SLC or DRAM), but I'm still learning. Awesome results from Jens there...

wtallis 6y ago
Enterprise SSDs often (but not always) reserve more spare area out of the pool of flash on the drive, which helps a lot with sustained write speeds, especially random writes; the garbage collector is under less pressure to free up erase blocks for new writes. Consumer SSDs use SLC caching which allows for much higher write speeds until that cache runs out, but then the drive is stuck with the job of cleaning up that cache while also still handling new writes. So for the same amount of raw NAND capacity and same usable capacity, an enterprise drive that doesn't do any SLC caching at all will tend to have a better long-term write speed than the post-cache write speed on a consumer drive.