PAE and large page file

[makkapakka]

I've currently got a file server that twice a day has performance issues.
The file servers within my infrastructure should all be configured the same.
But I have noticed that the server suffering from performance issues is the only server to have the /PAE switch enabled even though it only has 4GB of physical RAM.
It has also been configured with a pagefile 3x the amount of physical RAM, therefor pagefile=12288mb, whereas the other file servers have a pagefile of 4096.
Therefore my question is, can PAE functionality on servers that don't have more than 4gb of RAM actually cause performance issues?
Also, is the 3x physical ram pagefile a bad idea?
Paging is high, but when the server starts hanging, the pages/sec counter actually drops!

Any comments appreciated

 

[Roadki11]

I dont see the /PAE switch causing a problem, ive actually had to use it on systems with 4gb of ram just so the OS would use and see all 4gb. Without the /PAE switch some systems only see about 3.1 or 3.4gb of ram, no clue why. As for the page file, it seems excessively large to me, ive never had to make a page file larger than the physical ram. I would wonder what your disk I/O looks like when the system starts "hanging", perhaps you need to move the page file off the system drive, you didnt state where it is currently. I would also look for memory leaks, file servers shouldnt use a great deal of ram, unless the server is more than a file server? Here is a good link explaining page files that might help:

http://www.petri.co.il/pagefile_optimization.htm

RoadKi11

"This apparent fear reaction is typical, rather than try to solve technical problems technically, policy solutions are often chosen." - Fred Cohen

 

[makkapakka]

RoadKi11,
Thanks for your reply. The pagefile is located on d:.
I'm going to reconfigure it to 4096 and take off the PAE functionality.
I realise that without PAE the server properties will probably show up 3.2Gb of ram, I believe its something to do with the bios and memory mirroring, and that PAE or reconfiguring the BIOS will enable the OS to see the full monty.
I'm just thinking that the PAE kernel that is loaded when the /PAE switch is configured, may have additional overheads, especially when its full funtionality is not needed (machine doesn't have over 4gb RAM).

 

[58sniper]

Just a thought, but is shadowcopy performing it's work when the two slow periods hit?

Pat Richard MVP
Plan for performance, and capacity takes care of itself. Plan for capacity, and suffer poor performance.

http://www.ucblogs.net/blogs/exchange/

 

[makkapakka]

58sniper,

The volume shadow copy service isn't running on the problem server.

I've taken PAE funcitonality off the box and reset the pagefile to the size of the physical RAM. Had to try something!

 

[xmsre]

What the /PAE switch does do, is cause each page table entry to consume twice as much RAM. This effectively cuts the number of available PTEs in half. PTEs are important on a file server because they are used by kernal mode device drivers, like and HBA or RAID driver, as pointers to buffers. Try monitoring the memory counter Free System Page Table Entries.

A file server uses most of the RAM on the box for system cache. There is no one application that consumes a large amount of RAM. This means that on the properties of the server, advanced tab, performance settings, you want to check the radio buttons for background services and system cache. You also don't want the /3gb switch in the boot.ini. Your pagefile sould be 1.5 times physical RAM.

The reason you end up running the PAE kernal is really mainly cosmetic. PCI Express cards map a region of memory lower than the 4GB boundary. This means a server with 4GB of RAM will report 3.5 or 3.25GB if it has a couple of PCI Express cards in it. If you put the /PAE switch in the boot.ini, then the rest of the RAM gets mapped above the 4GB line and the server reports 4GB. It doesn't give any more memory to kernal mode and doesn't improve the performance of your system. So why bother? Did you really intend to degrade sever perfomance just so it reports 4GB?