Memory Usage Optimizations
As described in the Resource Utilization section your labs can consume a large amount of real and virtual memory. The “ghostios” and “sparemem” options were added to address both of these issues, respectively.



The Ghostios option can significantly reduce the amount of real host RAM needed for labs with multiple routers running the same IOS image. With this feature, instead of each virtual router storing an identical copy of IOS in its virtual RAM the host will allocate one shared region of memory that they will all utilize. So for example, if you are running 10 routers all with the same IOS image, and that image is 60 MB in size you will save 9*60 = 540 MB of real RAM when running your lab. Enabling ghostios is as simple as specifying “ghostios = true” in your network file. This option can be used in several places:

If used at the top level, ghostios is applied to all router instances in the lab
If used at the defaults section (e.g. “[[7200]]”) it applies only to that model of router on that dynamips server
Note that ghostios (and all other top level parameters for that matter) cannot be specified at the server level. They will be ignored. ghostios also cannot be specified at the router level


Typical usage is to specify “ghostios = true” at the top level. Dynagen is smart enough only to use ghostios if there is more than one router using the same IOS image.



When enabled, you will notice additional files in the same directory as you router nvram files with names like “c3660-ik9o3s-mz.124-10.image.ghost”. This is the mmap’ed file that contains the shared memory region. The other files typically created with a router instance are created as well (log, nvram, and possibly bootflash files).



Measuring the amount of host memory saved with ghostios can be a little tricky due to the complexities of memory management in modern OSs. See this sticky post in the General section of Hacki’s Forum titled “Understanding memory usage and RAM Ghosting: for the gory details.



The “sparsemem” feature does not conserve real memory, but instead reduces the amount of virtual memory used by your router instances. This can be important, because OS limits a single process to 2 GB of virtual memory on 32-bit Windows, and 3 GB on 32-bit Linux. For example, on Windows, after the VM space used by cygwin and other libraries dynamips depends on, this only leaves room for 4 router instances @ 256 MB each! Enabling sparsemem only allocates virtual memory on the host that is actually used by IOS in that router instance, rather than the entire amount of RAM configured. This can allow you to run more instances per dynamips process before you have to resort to running multiple dynamips processes. See this FAQ item for more info on this issue.



Neither ghostios nor sparemem are enabled by default, so you must turn them on with:



ghostios = true

sparsemem = true



in your network file. If you use ghostios, the shared memory will be memory-mapped no matter what your mmap setting is. If you enable sparse-mem, no memory mapping will occur for router memory. You can choose to use ghostios or sparsemem separately or together.



Here is an example network file with typical ghostios and sparsemem usage – configured at the top level so that they are applied to all router instances in the lab:



model = 3660

ghostios = true

sparsemem = true



[localhost]

      

      [[3660]]

      image = \Program Files\Dynamips\images\c3660-ik9o3s-mz.124-10.image           



      [[router r1]]

      fa0/0 = sw 1      # Note that you can use two letter interfaces names

                        # for increased clarity if you wish

      [[router r2]]

      fa1/0 = sw 2

      

      [[router r3]]

      fa1/0 = sw 3



      [[ETHSW sw1]]

1 = access 5

2 = access 25

3 = access 35

4 = dot1q 1 NIO_gen_eth: NIO_gen_eth:\Device\NPF_{B00A38DD-F10B-43B4-99F4-                                   B4A078484487}



原来是自动式的。晚上下班后去试验一下。