Virtual memory required by SAP system component?
ok, ok, I know there is already a link mentioning this Virtual Memory Required by SAP System Components
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 replied
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.