Server slows to a crawl when copying accounts from remote server

I'm migrating websites from an old cloud server account to a new one with a different host, using the built-in cpanel account migration.

The two servers connect with no problems, and the files do eventually move across, but the transfer speed is stuck at 0.1345 M/s so the transfer takes hours and hours - and more seriously, everything on the new server seems to slow to a complete crawl while the copy is happening. Fine again as soon as the copy is finished.

System information on new server says:
Server load 0.12 (1 CPU)
Memory Used 12.91% (512,992 of 3,974,524)
Swap Used 0% (0 of 6,291,448)

So it doesn't look like the slowdown is because server resources are anywhere near used up (the old server is performing fine)

I tried a Copy Multiple Accounts, but it took about 48 hours to complete, which is not much use when a couple of the sites are small forums and online shops so have posts and orders coming in. But even single account copies are taking a couple of hours per account, and I have 40 of them to move.

Should the rest of the server freeze up when copying is occurring? Any ideas why the transfer speed is so low?

 

Thanks! I've tried moving large files using SFTP, and that doesn't have the same effect. If I move a big file onto the new server using sFTP, then OK, the transfer is open for a while as the data moves across, as you'd expect but everything else on the server continues to respond as quickly as normal.

I can see that the network connection between Old Server and New Server might not be optimal, but I can't understand why New Server would suddenly start responding very slowly when doing something completely unrelated to the copy operation - eg, showing me a web page on another account, or displaying WHM pages.

Surely while the data is copying across, that should be happening in the background - the server isn't doing anything much with it, and should be able to carry on with normal operations at the same time?

 

So far as I can see, there is almost no load on New Server. It was showing this behaviour before any of the sites hosted on it had actually gone live, so it had generous amounts of disk space, memory, bandwidth, and almost nothing using it, apart from Cpanel doing a copy at a measily 0.1345 M/s and me, checking web pages and trying to view stuff in WHM.

Can I take it from that reply that WHM would not normally take 20+ seconds to render a page when there is one copy occurring, and no other load? My new host is saying the problem is network connection between old and new server, but I don't see how that would slow everything else the server is doing so acutely.

 

Thank you so much to everyone who replied to this thread.

With the information you gave me, I had the confidence to go back to my new hosting provider about this.

They had originally told me that the slowness must be a network issue on the wider internet, but after chasing them up about it several times and refusing to take 'we can't see the problem' for an answer, it turned out that the port on the new server was stuck at 1Mbps. They were able to resolve this and the server is now performing very nicely.