Samba performance problem over a radio link.

David Collier-Brown David.Collier-Brown at
Thu Jun 8 15:31:17 GMT 2000

Marco wrote:
| We have a performance problem over a 2 Mbits radio link.

>From your message, it looks like this is what you have, in
the same units: please correct me if this isn't right, as
I'm really reduced to guessing from your description...

Description				KB/S	Kbit/S	Mbits/S	% of max
Theoretical Max. 100 Mbit/S Eth.	12500	100000	100	100
local smb read, win9x			 5000	 40000	 40	 40
local smb read, win9x to NT server	  160	 1280	  1.28	  1.28

	This can't be true...

Theoretical Maximum, 2Mbit/S radio	250	2000	2	100
remote smb read, win9x			 70	 560	0.56	 28
remote ftp read, win9x			100	 800	0.8	 40
remote smb read, NT			100	 800	0.8	 40

	This looks plausible.

	I'm going to assume you want to know why Samba 
	with win9x clients is slower than ftp and NT clients
	over the speed-limited link.

	I **think** that the win9x SMB client program is not
	as good as packing lots of no-response-required
	operations into packets as the NT SMB client, and this
	shows up strongly on the speed-limited network. The
	client send a request, and starts waiting for an ACK.

	This is called "stop-wait" processing, for obvious 
	reasons (;-)) The desired behavior is to send a bunch 
	of requests and never wait. 

	Playing with the receive window will allow the sender to 
	send as many packets, containing SMBs, as possible, but the
	SMB protocol can defeat this.  I suspect that's why the
	improvement from playing with rwin levels off suddenly.

	TCP gurus, do please chime in!

	I think you might try two experiments: tuning the TCP for 
	large file throughput (normally not recommended) and turning
	off raw read/write (ditto).

	In three separate experiments, try
		read raw = no
		write raw = no

	If any causes a significant improvement, please tell
	the list: these are contra-intuitive approaches...

	Once we're past this, we'll look at SO_SNDBUF= with large values.

David Collier-Brown,  | Always do right. This will gratify some people
185 Ellerslie Ave.,   | and astonish the rest.        -- Mark Twain
Willowdale, Ontario   | //
Work: (905) 415-2849 Home: (416) 223-8968 Email: davecb at

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