Virtual memory required by SAP system component?

[former_member211576]

Hi experts,

  ok, ok, I know there is already a link mentioning this

I just want to confirm this sizing is correct. According to Cameron's guidance(note 1612283), 2 * E2680(16 cores) and 384 GB DRAM can run 6-8 dialog instances per server. Karl-Heinz Hochmuth recommends

Page file sized needed = total virtual memory - RAM and

ABAP dialog instance = 2 times PHYS_MEMSIZE.

  That's to say, if I have 384GB DRAM, I should allocate about 384GB pagefiles size for 6-8 SAP dialog instances(each instance with PHY_MEMSIZE=32000) and that's sufficient, right?

  I remember SAP recommended pagefiles size should be 3x - 4x of physical memory size before and that is invalid now, right? Also, It is not necessary to allocate very large pagefiles even though I have 8 SAP dialog instances running concurrently, correct?

[karl-heinz_hochmuth · Accepted solution]

Hello Dennis,

some questions about your sizing:

How many dialog instances do you want to run in parallel on one Windows system?

Which Windows version do you plan to use?

Virtualized or on a physical box?

How many CPU cores do you have? (Hyperthreading turned on)

How much RAM do you have?

How many work processes do you plan to use (per dialog instance)?

Test / dev systems or productive usage?

Best regards,

Karl-Heinz

[former_member211576 · Accepted solution]

Hi Karl-Heinz,

How many dialog instances do you want to run in parallel on one Windows system?

>6-8 SAP instances per server.

Which Windows version do you plan to use?

>Windows Server 2012.

Virtualized or on a physical box?

>Physical box.

How many CPU cores do you have? (Hyperthreading turned on)

>32 cores.(2 * E2680v3)

How much RAM do you have?

>384GB

How many work processes do you plan to use (per dialog instance)?

>50-60 work processes.

Test / dev systems or productive usage?

> productive usage

[karl-heinz_hochmuth · Accepted solution]

Hello Dennis,

then try the formula from the mentioned document.

ABAP Dialog Instance, virtual memory requirement:

1 - 2 times PHYS_MEMSIZE + 2.5 GB + 250 MB per work process

In your case, let's first check the sizing (I will now calculate with 6 dialog instances):

6 instances x 50 (planned work processes) = 300 total

SAP recommends 4 - 5 workprocesses per core.

300 workprocesses / 6 = 60 cores  (you should have ...)

Ok, that only a remark for you. If the most of the work processes are most of the time idle, nothing happens.

Now take a look at the virtual memory requirement. For productive usage we calculate in above formular with 2 times PHYS_MEMSIZE:

For one instance:

64 GB + 2.5 GB + 12.5 GB  => 79 GB

Let's add together:

6 instances:           474 GB

Windows:                20 GB    (~ 5 % of RAM)

Third-party:               ?  GB    (tools, antivirus-scanner, backup, ???)

====================================================

Sum                       494 GB 

virtual memory minus RAM = pagefile size

=> 494 - 384   =   110 GB

So, your pagefile should be AT LEAST 110 GB.   (for 6 instances)

To answer your question:

1 fast RAID 1 with 600 GB net is very nice. Set the pagefile of Windows to a fixed size of 200 GB (or if you plan to install more instances and the workload cannot be really predicted) to 300 GB.

Do not use the "dynamically configured" pagefile settings (controled by the Windows OS). We had several issues in the past where the Windows OS wasn't fast enough to increase a dynamically configured pagefile and the work processes run out of virtual memory - during start up phase.

Best regards,

Karl-Heinz

[former_member211576 · Accepted solution]

Hi Karl-Heinz,

  Thanks a lot for your very detail calculation. Our current production system has 18 application servers now and each application server has 59 work processes configured. That is 1062 work processes in total. However, the active work processes are around 90 - 100 work processes. Anyway, our managers, developers and users prefer they have their own dedicated application servers to run their jobs.

  By the way, why do I care so much about this issue? Our old productive application server has 32GB memory and because there is only one dialog instance running. I did not configure PHYS_MEMSIZE manually. Sometimes our managers and users might want me to create additional application server for QAS for testing purposes. I think maybe I did not configure PHYS_MEMSIZE for each SAP dialog instance(PRD and QAS) accordingly, sometimes I have to create 3x - 4x pagefiles size to start additional(for QAS) dialog instance.

  In summary, if PHYS_MEMSIZE are configured correctly,

"number of dialog instances * PHYS_MEMSIZE for each = total PHYS_MEMSIZE on one server"

"total PHYS_MEMSIZE should be less than main memory"

"pagefile size should be less than or equal to main memory size"

Page file sized needed = total virtual memory - RAM and

ABAP dialog instance = 2 times PHYS_MEMSIZE.

Only 110GB pagefile size are required. So if I configure pagefile size equals to 1x of main memory(384GB), it should run without any problems even in heavy workload like month end closing.

[karl-heinz_hochmuth · Accepted solution]

Hello Denis,

the answer is: Yes a 384 GB pagefile should be sufficient. You can check this anytime, e.g. with the "systeminfo" command. There you will find information how much RAM is currently used and how much virtual memory is currently used.

You can also use TaskManager or tools from www.sysinternals.com - of course.

One comment to your old configurations:

If you want to add another SAP dialog instance on a Windows OS where already one SAP instance is running you MUST specify the PHYS_MEMSIZE parameter in instance profile. This will be made e.g. if you upgrade a SAP system, a so called "shadow instance" will be installed during upgrade and this instance will be usually run with PHYS_MEMSIZE = 50%.

If you don't set PHYS_MEMSIZE to a lower value than RAM, than it is EQUAL to RAM.

Which means, that you need huge pagefiles to simply START your instances.

This has something to do with the SAP memory model and how memory address space will be allocated AND reserved.

Best regards,

Karl-Heinz

[Sriram2009]

Hi Lee

Depend on your SAP system usage & requirements. At the very beginning time you can define the pagefile size for each VM should be 1.5 to 2 or 2.5 max time of physical memory(32 GB per vm). depend on usage you can either add more or reduce the size of the pagefile. and also you can refer the SAP Note for other parameters

88416 - Zero administration memory management for the ABAP server

BR

SS

[former_member211576]

Hi SS,

   Thanks for your reply. Of course, I know pagefile size can change dynamically. I ask because I have to know how many 600GB SAS HDDs should I buy. Is it  two for one RAID 1 group or eight for four RAID 1 group if 3x-4x pagefile size of 384GB physical memory are required.

[Sriram2009]

Hi Lee

Once again depend on your SAP system requirements. You can refer the SAP Solutions on VMware Best Practices Guide and also you can contact your SAN vendor to design the Storage space for your environment.

http://www.vmware.com/files/pdf/solutions/sap/SAP-Solutions-on-VMware-Best-Practices-Guide.pdf

BR

SS