…ok, TrueNAS SCALE ( Dragonfish-24.04.2.2 ) on bare metal. From every H/W PC I can see the same: I can write to the NAS at top speed but read at 1/2 or 1/3 of the speed.
It may be the NIC. But the same happens within a VM.
…I can understand copper vs. fiber or anything facing out hardware wise but in a VM with VirtIO NIC and drive ?
I read from a pool/dataset ( of 1 NVMe ) and the VM is in another pool/dataset ( a 2 mirror NVMe ). So is not that am reading and writing to the same drive ( that been NVMe would not be a limiting factor anyway ) but, explaining for you to get a good picture of what is the I’ve got going.
What can it be ?
Just to have an idea of the NVMe speed, in the VM the read is 6k and the write is 5k. That is not drive speed that limits the bandwidth.
There are some other threads here in the forum with similar problems (read speed) and it seems it has to do with the drive configuration and how ZFS it handles.
It’s my personal opinion, a lot of other things are possible, including the NIC.
See other recent threads about how NOT to read simplistic performance measures.
For starters, for both reads and writes you are probably NOT measuring the disk speed. For example, reads may be coming from memory (ARC), writes may be being made to memory (asynchronous).
Performance measurement require you to understand in detail what the software is doing and to tweak both the operating environment (ARC caching and read-ahead) and the measurement methodology in order to get meaningful hardware measurements.
