On 10/7/25 14:08, Tomas Vondra wrote: > ... >>>>>> I think doing this kind of measurement via normal SQL query processing is >>>>>> almost always going to have too much other influences. I'd measure using >>>>>> fio >>>>>> or such instead. It'd be interesting to see fio numbers for your >>>>>> disks... >>>>>> >>>>>> fio --directory /srv/fio --size=8GiB --name test --invalidate=0 >>>>>> --bs=$((8*1024)) --rw read --buffered 0 --time_based=1 --runtime=5 >>>>>> --ioengine pvsync --iodepth 1 >>>>>> vs --rw randread >>>>>> >>>>>> gives me 51k/11k for sequential/rand on one SSD and 92k/8.7k for another. >>>>>> >>>>> >>>>> I can give it a try. But do we really want to strip "our" overhead with >>>>> reading data? > > I got this on the two RAID devices (NVMe and SATA): > > NVMe: 83.5k / 15.8k > SATA: 28.6k / 8.5k > > So the same ballpark / ratio as your test. Not surprising, really. >
FWIW I do see about this number in iostat. There's a 500M test running right now, and iostat reports this: Device r/s rkB/s ... rareq-sz ... %util md1 15273.10 143512.80 ... 9.40 ... 93.64 So it's not like we're issuing far fewer I/Os than the SSD can handle. regards -- Tomas Vondra
