Recommended pagefile/swapfile size for IA64 with v8.3

[Dmitry V. Sinelnikov]

Hi all

I have an IA64 system (HP rx4640, 4Gb RAM ) running under OpenVMS V8.3-1H1. Would like to know if there are any recommended values for swap/page files? At the moment they have the following:

Directory SYS$SYSROOT:[SYSEXE]
PAGEFILE.SYS;1 439.45MB
SWAPFILE.SYS;1 57.22MB

More than sure it’s too small. AFAIK, for Win OS it’s recommended to set pagefile twice as large as RAM size. What about OpenVMS on IA64?

Any feedback is appreciated,

Best regards,
Dmitry Sinelnikov

[Volker Halle · Accepted solution]

Dmitry,

trust AUTOGEN.

Make sure there are no PAGEFILE=0 and SWAPFILE=0 statements in MODPARAMS.DAT and run

$ @SYS$UPDATE:AUTOGEN SAVPARAMS TESTFILES FEEDBACK

AUTOGEN will then tell you about the suggested size of your page and swap file.

Volker.

[Steven Schweda]

> [...] What about OpenVMS on IA64?

Pretty much the same as VMS on any other
hardware: Make them as big as they need to
be.

I'd expect the VMS installation procedure to
create files big enough to let the system
start. After that, everything depends on the
workload. SYS$UPDATE:AUTOGEN.COM can offer
advice on a system which has been running for
a while. INSVIRMEM errors suggest that you
need a bigger page file.

> [...] 4Gb RAM [...]

> PAGEFILE.SYS;1 439.45MB

440MB is not much of a boost over 4GB. But
if all your work fits into 4GB, then you
wouldn't need much.

HELP SHOW MEMORY /FILES

[The Brit]

Dmitry,

It obviously depends on your apps, users, physical memory, etc., however you can monitor your page/swap files in real time, using the command

$ show mem/files
System Memory Resources on 16-OCT-2009 09:53:44.57

Swap File Usage (8KB pages): Index Free Size
DISK$I64_V831H1:[SYS0.SYSEXE]SWAPFILE.SYS
1 6248 6248

Paging File Usage (8KB pages): Index Free Size
DISK$ND17:[SYS0.SYSEXE]PAGEFILE.SYS;1
249 624992 624992
DISK$ND16:[SYS0.SYSEXE]PAGEFILE.SYS;1
250 624992 624992

or use

$ monitor page

and watch the size of the modified list relative to the SYSGEN parameter MPW_HILIMIT

Dave

[Jon Pinkley]

Dmitry,

Having more RAM doesn't necessarily mean you need a bigger page/swap file. Given the same load, if you have more RAM you will actually need less pagefile space.

That said, it is better to have more pagefilee than needed than too little, as the system will eventually hang, if you memory demand exceeds your RAM plus your pagefile.

The pagefile is only used when the demand for memory exceeds what is available. In recent versions of VMS it is possible to run with no pagefile, but there are some old hard coded assumptions that there will be pagefiles around.

Here's an example: SYS$COMMON:[SYS$STARTUP]VMS$CONFIG-050_JOBCTL.COM computes the page file max (50% of total, minimum of 40960) on Alpha, I am not sure if IA64 does something different, I don't have one.

The point is that there is no meaningful correlation between RAM and Pagefile size. The pagefile size is much more dependent on the memory demand in excess of available RAM placed on the system.

As others have stated, let AUTOGEN look at what the demand has been, and let it make a recommendation.

Jon

[Andy Bustamante]

I'd like to remind you to check the size of your dumpfile as well. As Volker points out, set SWAPFILE, PAGEFILE and DUMPFILE to 0 in modparms.dat. This will prevent fragmenting these files from each run of AUTOGEN. See System Manager's Manual vol 2 at http://h71000.www7.hp.com/doc/82final/aa-pv5nj-tk/aa-pv5nj-tk.html for more information.

Andy

[Hoff]

Save FEEDBACK when you SHUTDOWN. Trust AUTOGEN.

Here's a general description of the implementation of virtual memory.

http://labs.hoffmanlabs.com/node/228

On OpenVMS, the pagefile and swapfile and backing section files are how the amount of physical memory that is (apparently) present in the box is increased. So if you find your particular application load needs more physical memory, you either need to increase its working set, or add more physical memory, or you need more pagefile, or some combination.

But as for recommendations, that is dependent on your particular load. Anyone that's performed typical OpenVMS system management operations has run an OpenVMS box with no pagefile, for instance.

[John Gillings]

Dmitry,

Disk space is cheap. Downtime is VERY expensive. Make sure you have sufficient pagefile space that downtime because of virtual address space depletion is effectively impossible. With disk space as cheap as it is consider investing (say) $10 in disk space for page file? Very cheap insurance. There are no simple rules of thumb, since it all depends on your workload.

With modern memory sizes, swap file is probably never used. SWAPFILE.SYS can only be used for swapping. PAGEFILE.SYS can be used for both (but with slightly higher overhead for swapping). Since swapping is likely to be a very rare event, you could go without a swapfile. On the other hand a few MB isn't going to break the bank.


re: Volker

>trust AUTOGEN.
>
>Make sure there are no PAGEFILE=0 and >SWAPFILE=0 statements in MODPARAMS.DAT and >run

Interesting! My advice is exactly the opposite of Volker. Maybe Hoff and Hein can come up with even further conflicting advice? ;-)

I never trust AUTOGEN to size system files, and recommend MODPARAMS.DAT set PAGEFILE=0, SWAPFILE=0 and DUMPFILE=0. This is mainly because AUTOGEN likes to change the file size, whereas I'd rather they kept their allocated size. In particular, I never want AUTOGEN to *reduce* a size I've specified.

Remember, AUTOGEN's job is to make a bootable system, not an optimal one, and it can't guess what your virtual memory requirements will be, and allocation algorithms haven't been updated in years (decades?), time over which the economic trade-offs have changed considerably! I'd guess that when AUTOGEN was last updated, the amount of RAM you have would have been considered a very large disk! The sizes you've quoted are a good example. They're a joke! Just compare the total cost of your system (order ~$K) against the investment in disk space for page and swap space (order cents).

Read the AUTOGEN recommendations, and make sure your allocation is higher (in most cases add at least one 0, if not two!).

All that said, it's not uncommon to see systems these days that don't touch their page file at all. I remember a case where it took a whole week to notice that a non-shadowed system disk had been popped out of its rack. The system ran from resident images and cache, never touching the page or swap files! (I'm still not sure if that's illustrates a good feature of OpenVMS or a very bad one!)

[Hoff]

Folks that are sufficiently familiar with and that are skilled with OpenVMS operations can and variously do lock AUTOGEN out of re-sizing the PAGEFILE and SWAPFILE and DUMPFILE files but - given the question here and given the likely requirement to quickly get the server into the right file size range? Yes, I trust AUTOGEN (particularly with FEEDBACK) to get a server into the right range; as a good first or second-order approximation, particularly as you (or AUTOGEN) learns about the load.

Or yes, if you have several "spare" (RAID-protected would be preferred) disks around, you could dedicate the whole of several of those disks to the PAGEFILE (and a runt swap file, and a dumpfile sized for a reasonable hunk of 4 GiB) and move on. This is the "throw hardware at the problem" approach, and that can be expeditious given disk prices these days.

[Volker Halle]

re: John & PAGEFILE=0

I also suggest to use PAGEFILE=0, SWAPFILE=0 and DUMPFILE=0 in MODAPRAMS.DAT, but to get the TESTFILES suggestions, one has to temporarily disable those lines.

So we are in synch with our suggestions and I should have added the word 'temporarily' to my response.

Volker.