Andy Smith wrote: > Hi Mick, > > On Wed, Dec 23, 2020 at 12:55:58AM +0000, mick crane wrote: >> I have a buster PC and a bullseye PC which are both supposed to have >> gigabyte network cards connected via a little Gigabyte switch box. > > "gigabyte" is not a network speed. You probably mean gigabit; that > is 10⁹ bits per second, i.e. 1000 * 1000 * 1000 bits per > second. > > GNU units can be useful to indicate what you can expect: > > $ units gigabit > Definition: 1e9 bit = 1e+09 bit > $ units megabyte > Definition: 1e6 byte = 8000000 bit > $ units 1gigabit/sec megabyte/sec > * 125 > / 0.008 > > So on a gigabit network the absolute maximum you could expect is > 125MByte/sec. Note that's SI prefix mega- meaning million bytes, not IEC > binary prefix MiB, meaning 1024 * 1024 bytes. > >> Transferring files between them, I forget which shows the transfer speed >> per file, either scp or rsync the maximum is 50 Mbs per file. > > I shall assume that "50Mbs" means "50 megabytes per second" and not > what it literally means which is "50 Megabits per second", a > quantity one eighth as much. > > scp and rsync add a lot of overhead, especially when operating on > relatively small files. On a gigabit network I find myself lucky to > get more than about 90MB/sec through ssh or rsync-over-ssh. > > So I find 50MB/s plausible. > >> Would you expect that to be quicker ? > > Not really. > > To get a more realistic idea of your network's performance use > something like Iperf. You still won't see the full 125MB/s but I'd > expect it to go over 100. > > If you are trying to transfer files as fast as possible and don't > need encryption, consider netcat. If you do need the encryption of > ssh, but don't need the features of rsync, then "tar | ssh" will be > a little faster. > > On a low latency network (like your local network) at gigabit+ > speeds, compression won't make things faster. > > Cheers, > Andy
fully agree with you regarding the units and the rest. SCP displays transfer rate in MB/s not Mbps, so the expected maximum on 1Gbit network would be 125MB/s I managed to get above 50MBs on the home network (with luks+LVM using SCP) only after I replaced the old discs. I guess it depends on the machine and disks. I bet I'll get even higher speed (close to 125MB/s) if I would use SSDs. The point is - it is much more than the mere calculation - there are boards with different architectures, where you could have a small bottle neck here or there, memory and other things too.
