[THIN] Re: SMB Current Commands and SMB tuning

  • From: Dan Dill <DanD@xxxxxxxxxx>
  • To: "thin@xxxxxxxxxxxxx" <thin@xxxxxxxxxxxxx>
  • Date: Tue, 16 Nov 2010 15:52:32 -0800

So those stats were pulled during the afternoon at peak load (which is light 
for our servers, around 20-25 sessions).  I kept an eye on it over the course 
of an hour or two and saw that same pattern, flat with a couple of slight 

I do appreciate those links, I did read through those before sending the email 
to the list and agree that those have are good resources.

I did some testing last night on a Citrix server without MaxCmds set in the 
hops of understanding exactly how it works under the hood.  The citrix blog 
article on SMB 
 seemed to suggest 'current commands' = smb mpx limit which didn't seem to be 
the case in my environment.

On to the late night very unofficial test: Citrix is hitting CIFS on a Netapp 
array with MPX set to 126 so the session was established with the default 50 
limit (from the client).  Off the start it seemed to take up 2 'commands' just 
from a user being logged in.  With 50+ directories opened in windows explorer 
it seemed to take up a "current command" for each folder opened, until around 
50 after which is seemed to be re-using slots or something.  It didn't scale up 
linearly from that point.  Opening 50+ individual files used just one more 
'command' on the server.  So 50 files = 3 commands, 50 directories = 52 
commands.  I tested 50 files both in the same directories and each in its own 
directory (yay for powershell).  I never did hit a point where a file or folder 
open request failed, though I only tested up to about 75 of each.

After tuning the server (MaxCmds), opening more than 50 folders resulted in a 
'command' for each folder, scaling linearly.

So my guess is that connections to folders and files are counted in that 
perfmon counter but that when it hits the negotiated limit the server begins to 
re-use or scavenge connections which can cause performance problems.  I wonder 
if this would only be a hard limit if your MaxCmds was less than the number of 
sessions (or users?) on the given machine perhaps?  Or perhaps it's only a 
problem when 50 files are opened at a given time from that machine and not 50 

So unfortunately I didn't satisfy my question of what exactly that counter is a 
reflection of and how that relates to MaxCmds.  I'm just going to roll that 
setting across the Citrix farm even though I'm not so sure it will provide any 
benefit or in what circumstances it would provide benefit.  So maybe this was a 
snipe hunt, maybe not.

Andrew I fully realize the possibility of there being a problem with this and 
it not being reported.  It's also possible that this isn't a problem and 
changing these settings will make no difference in my environment and I'm just 
wasting my time.  It's better to err on the side of performance and since this 
is quite mainstream the changes will be made.

Thanks for the help everyone.

Dan Dill |Systems Engineer | Harsch Investment Properties

From: thin-bounce@xxxxxxxxxxxxx [mailto:thin-bounce@xxxxxxxxxxxxx] On Behalf Of 
Andrew Wood
Sent: Tuesday, November 16, 2010 12:03 AM
To: thin@xxxxxxxxxxxxx
Subject: [THIN] Re: SMB Current Commands and SMB tuning

Joe's figures are the ones recommended - bear in mind you need to change the 
file servers as well

To answer your question Dan, perhaps your servers are fairly flat because the 
SMB commands were relatively constant when you did the test and by the looks of 
it, operating relatively well. When did you do the test? During the day? First 
thing in the morning? At the end of the day? Mid afternoon? If you were to set 
off some big file copies on a server - does the number go up? If you tune the 
values on the TS servers and the file servers, does the file copy take less 

What are those perfmon values on your file servers/domain controllers? What is 
the maxmpxct value on the file servers those citrix servers communicate with?

"I've got an un-tuned server that hit 57 today without any reported issues" - 
its possible you did have a problem, it slowed for a second or two, or wasn't 
as responsive as it could have been. "No Issues" often equals "no one said 
anything to me" - Maybe no one would have reported it because, unless it was 
prolonged, or regular, or stopped your CEO from checking Facebook few would 
raise a helpdesk call along the lines of "5 minutes ago the citrix server 
paused for a second or two, but its ok, it got better"

This is a great article to read - which details SMB tuning across Windows 2003 



From: thin-bounce@xxxxxxxxxxxxx [mailto:thin-bounce@xxxxxxxxxxxxx] On Behalf Of 
Joe Shonk
Sent: 16 November 2010 05:01
To: thin@xxxxxxxxxxxxx
Subject: [THIN] Re: SMB Current Commands and SMB tuning

Here are the recommended settings from Microsoft: 

Microsoft Recommended Optimization Settings for Terminal Service
                MaxWorkItems = 8196
                MaxMpxCt = 2048
                MaxRawWorkItems = 512
                MaxFreeConnections = 100
                MinFreeConnections = 32

                MaxCmds = 2048
                RegistryLazyFlushInterval = 60


From: thin-bounce@xxxxxxxxxxxxx [mailto:thin-bounce@xxxxxxxxxxxxx] On Behalf Of 
Dan Dill
Sent: Monday, November 15, 2010 6:11 PM
To: thin@xxxxxxxxxxxxx
Subject: [THIN] SMB Current Commands and SMB tuning


I've been digging into SMB tuning for our PS 4.5 Server 2003 x64 citrix farm as 
our farm currently doesn't have MaxMpxCt or MaxCmds set on our servers.  I am 
confused by the results of the Redirector\Current Commands output in perfmon.  
That counter is defined as: "counts the number of requests to the Redirector 
that are currently queued for service" however the graph over time is quite 
flat when I could expect a queue graph to look spikey.  Is that counter a 
combination of the outstanding SMB requests plus something else?

I've got an un-tuned server that hit 57 today without any reported issues when 
I would have expected it to cap at 50 or start exhibiting problems at that 

Anyone know why those counters are fairly flat?  Is there a better way to see 
if I'm hitting MaxCmds or do people just set it higher regardless?



Dan Dill |Systems Engineer | Harsch Investment Properties

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