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New Member

Cisco 3750 Stack - Terrible Performance Issues

I am having performance issues with 2x48P 3750 Stacked switches. Overall performance is really bad in all spects: VoiP, Server Transfers, SAN and VM traffic. This is an inherited site  and I am looking to improve network performance since it is terrible. By looking at some other forums my first impression is that stack is being overloaded with SAN and VM traffic. I am not sure if the Cisco stack is suited handle tons of traffic specially from the SAN and VM and I would like to have some advise.   See my attached outputs expert advise would be great.

Switch Ports Model              SW Version            SW Image

------ ----- -----              ----------            ----------

     1 54    WS-C3750X-48P      12.2(53)SE2           C3750E-UNIVERSALK9-M

*    2 54    WS-C3750X-48P      12.2(53)SE2           C3750E-UNIVERSALK9-M

Also i just noticed only on stack cable was installed and it shows as Half Speed. Would this also affect performance?

Stack Ring Speed        : 16G

Stack Ring Configuration: Half

Stack Ring Protocol     : StackWisePlus

Thanks in Advance.

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Gold

Cisco 3750 Stack - Terrible Performance Issues

Here are my recommendations:

1.  Upgrade your IOS.  It's buggy.

2.  Install the second stacking cable.

3.  Observe for any improvements.

4.  Remove SAN.

5.  Observe for any improvements.

9 REPLIES
Hall of Fame Super Gold

Cisco 3750 Stack - Terrible Performance Issues

By looking at some other forums my first impression is that stack is being overloaded with SAN and VM traffic. I am not sure if the Cisco stack is suited handle tons of traffic specially from the SAN and VM and I would like to have some advise.

Correct.  Cisco Catalyst switches are not designed to handle SAN traffic.  Period.  You want switch for SAN traffic?  It's Cisco Nexus.

Next, your IOS.  It's one of THE worst IOS.  Try 12.2(55)SE8. 

New Member

Cisco 3750 Stack - Terrible Performance Issues

Thanks I will start with taking off the SAN traffic out this stack. How about the the the situation with one stack cable. Would connecting the second cable help performarce and can this be plugged as a hot swap.

Silver

Cisco 3750 Stack - Terrible Performance Issues

Hi,

See this:

This is the maximum theoretical ring speed (bandwidth) for a Catalyst 3750 switch, by adding a second cable and complete the ring you should have 32 Gb/s of bandwidth.

32 Gb/s with a full or complete StackWise ring

16 Gb/s with an incomplete or open ring, only one StackWise cable on two switches in the ring

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/troubleshooting/switch_stacks.html#wp39498

Hall of Fame Super Gold

Cisco 3750 Stack - Terrible Performance Issues

How about the the the situation with one stack cable.

Not a smart idea.  Use two cables.

One cable means you're only operating at half the stackring speed.

Hall of Fame Super Gold

Cisco 3750 Stack - Terrible Performance Issues

Would connecting the second cable help performarce and can this be plugged as a hot swap.

It would slightly improve performance and it can be installed while the switches are powered on.

Hall of Fame Super Gold

Cisco 3750 Stack - Terrible Performance Issues

Here are my recommendations:

1.  Upgrade your IOS.  It's buggy.

2.  Install the second stacking cable.

3.  Observe for any improvements.

4.  Remove SAN.

5.  Observe for any improvements.

New Member

Cisco 3750 Stack - Terrible Performance Issues

Thank you all for your advise.

Super Bronze

Re: Cisco 3750 Stack - Terrible Performance Issues

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Posting

As noted in other posts, getting 2nd stack cable in operation will double bandwidth between stack members.  However, 3750 series are noted for insufficient port buffers to handle (well) transient bursts, so I would first suspect issues there rather than on the stack (but it's still worthwhile to get the 2nd stack port in operation.)

Look for packet drops on ports.  If there's much, check whether QoS is enabled.  If so, determine whether you need QoS.  If not, disable QoS.  If needed, you may need to tune buffer usage parameters.

Also on the 3750X series, the "uplink" ports have more memory for the number of ports than the copper ports do.  So if you have high drop rate ports (SAN devices?), if not already using them, move those ports to available "uplink" ports (if copper, you'll need copper SFPs).

Other alternative for very high usage gig ports, if possible, consider Etherchannel and/or 10g.

Leo's suggestion to upgrade IOS, besides addressing bugs, may (cough - NDA - cough) offer some other improvements.

Hall of Fame Super Gold

Cisco 3750 Stack - Terrible Performance Issues

Leo's suggestion to upgrade IOS, besides addressing bugs, may (cough - NDA - cough) offer some other improvements.

You really need to get that cough fixed, Joseph.  You've been having a lot of coughing fits lately. 

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