26 ms·
50 microseconds is a lot. I'm looking at disk read latency on a bunch of baremetal servers (nothing fancy, just node_disk_read.* metrics from node-exporter) and
by Nemo_bis 3y ago
50 microseconds is a lot. I'm looking at disk read latency on a bunch of baremetal servers (nothing fancy, just node_disk_read.* metrics from node-exporter) and one of the slowest fleets has a median disk read latency barely above 1 microsecond. (And that's with rather slow HDDs.)
- namibj 3y agoSamsung 980 Pro SSDs, the early generation ones (they seem to later have replaced them with a different, likely worse architecture), have average latency 4k reads of 30~70~120 microseconds for single queue/70% of the IOPS the 120us gets you/maximum parallelism before latency goes through the roof. The metrics you mention have to be pagecache hits. Basically all MLC NAND is in the double digit microseconds for uncontended random reads.
- Nemo_bis 3y agoThey likely are cache hits, indeed (any suggestion what other metrics would be more comparable?). Still, at the end of the day I don't care whether a disk operation was made fast by kernel caching or by some other optimization at a lower level, I only care about the final result. With public cloud virtualization there are more layers where something may go wrong, and good luck finding answers from Amazon or Microsoft if your performance turns out to be abysmal.
- deleted 3y ago[deleted]