Questions on 2960 Switch Memory

[pedro.alexandre]

Hi guys ! Hope someone can point me in the right direction.

We have 08 Cisco Switch model WS-C2960G-24TC-L running a 15.0(2)SE8 ( MD ) -25-MAY-2015 firmware version.  All of them are working with more than 80% memory processor.

show memory statistics
Load for five secs: 4%/0%; one minute: 10%; five minutes: 8%
Time source is NTP, 12:01:56.014 BSA Tue Apr 3 2018

                Head    Total(b)     Used(b)     Free(b)   Lowest(b)  Largest(b)
Processor    2704F2C    21991476    19241384     2750092     1006956     1648856
      I/O    2C00000     4194304     2659576     1534728     1374784     1515872
Critical     3876A00      859980          44      859936      859936      859936
Critical     2E5EA74      164020          44      163976      163976      163976
Driver te    1880000     1048576          44     1048532     1048532     104853

I didn't find any memory leak bug in this specific firmware version, although Cisco recommends an upgrade for a more recent version.  Version 15.2.2E7 ( MD ) - 14-JUL-2017. 

My questions are: 

01 - Is there a risk to run with that amount of process memory in used ?  The switch behavior is normal so far.

02 - Is that total amount of process memory too low ? Because I realized that some others switch models has much more process memory than this. 

03 - Am I able to do a Switch DRAM memory upgrade ?

Thank you in advance !!

-  Pedro Alexandre

[Reza Sharifi · Accepted solution]

Hi Pedro,

01 - Is there a risk to run with that amount of process memory in used ?  The switch behavior is normal so far.

Even though the switch's behavior is normal now, you may enable a new feature on the switch in the future and that could cause the switch to run out of memory.  So, I suggest you upgrade to what Cisco recommends.

02 - Is that total amount of process memory too low ? Because I realized that some others switch models has much more process memory than this. 

Hard to tell as every switch is different but an upgrade may help in general.

03 - Am I able to do a Switch DRAM memory upgrade ?T

No, the memory is not upgradeable.

HTH

[pedro.alexandre]

Hi Reza,

Thank you for your answers !

What's the minimum amount of process memory available do you consider be acceptable ?

Do you know if there is some Cisco Recommendation for that ?

Best Regards

Pedro Alexandre

[Reza Sharifi]

Hi Pedro,

Overall, the memory numbers for your switch looks good.

Load for five secs: 4%/0%; one minute: 10%; five minutes: 8%

 Looking at this, the average memory usage is 10% of the total which I think is very reasonable. Now, there may be a couple of areas that use more memory but other critical areas are not using much at all.

So, an upgrade may or may not help to lower the higher numbers.

Also, every Cisco device is different when it comes to memory and CPU usage and I don't think there is any recommendation as to what it should be. I usually start worrying when the total memory usage goes above 50%.

HTH

[pedro.alexandre]

Hi Reza,

I see !  Thank you very much for your help. 

Best Regards

Pedro Alexandre

[Joseph W. Doherty]

Generally most of the RAM is being used by the switch's IOS. That being the case, later IOS versions, which tend to have more features, are "larger" and need more RAM (hence the Cisco recommendation).

Some of the RAM, is being used by switch features, often RAM usage amount controlled by your configuration and your actual traffic. For a simple example, if you enable a logging buffer, you set its max size, and it will consume up to that amount of RAM.

[pedro.alexandre]

Hi Joseph !  I see your point.

Thank you for your contribution !

I took a look at the "Inside IOS Software Architecture" book to try to understand how the Cisco IOS manage the memory. My conclusion was: As long as there is physical memory available, the IOS will distribute and redistribute that memory between the logical pools.

So even it's saying there is only 10% of memory process available, the IOS will allocate more memory if needed, since it still have 90% of general memory available. 

Regards

Pedro Alexandre

[Joseph W. Doherty]

There is a "gotcha", though. If you run low on free RAM, due to fragmentation, you may not have a large enough block to provide a memory allocation request. IOS doesn't use a garbage collector.