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[Openvpn-users] Maximizing NetBIOS Performance

  • Subject: [Openvpn-users] Maximizing NetBIOS Performance
  • From: "Henric Rosvall" <henric@xxxxxx>
  • Date: Thu, 4 Oct 2007 10:55:36 +0200

Hi !
I've written a software that transfers the nightly backups to another location using NetBIOS (Windows File- and printer sharing) through a Open VPN-connection. We're talking massive amounts of data each night, which introduces a problem: Transfer speed.
At first I had a single thread that transfered all the files, but then I only got about 12% in average of the max speed, which translates to 1.2 MBit/s. The transferspeed-curve was also quite jagged.
So I rewrote some of the software, to make it multithreaded. After adding a second thread, I got it up to around 25%, but after that, adding more threads really doesn't make much of a difference - it only makes the transferspeed-curve a bit smoother for each thread added.
And here's the really weird part: I get around 25% per server. So if I transfer two files from one server, and two files from another server, it hits around 50%. 6 files from three servers makes it go to around 75%. This is true regardless of wether I use my own software, or if I just use the file explorer to transfer the files.
So it seems that the NetBIOS-protocol limits the amount of connections to one, and the added amount of transfer-threads maximizes the performance of that single connection. So my four threads have to share that single NetBIOS-connection, resulting in a stunted performance. At least that's my enterpertation of the problem. I know this might not be all that OpenVPN-related, but any hints on how to boost NetBIOS-performance by beeing able to make more than one connection (or some other optimization), would be greatly appreciated. I know for a fact that IIS is able to make one NetBIOS-connection / file that it monitors (which wreaked havoc with our fileserver when setting up our new Web Farm, causing about 500 simultaneous NetBIOS-connections (and Windows had a default limit at around 150 or somehting like that)), so it should be possible to do this programatically. I just dont know how.
Right now, the only solution I can think of, would be to create 3 virtual machines, all sharing the backup-drives, which would make me able to transfer the data using 4 connections, resulting in a maximized transferspeed. But that seems like a really bad solution (plus the fact that it would be difficult to make the software handle it in a good way, since it would see it as four separate backup-sets, and download each file four times, resulting in the same performance, or worse, than I have today)
Henric Rosvall