Re: transfer speed data

[deloptes <deloptes@gmail.com>]

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.