topic creating page and swap files in Operating System - OpenVMS

creating page and swap files

vmsserbo — Wed, 03 May 2006 14:18:26 GMT

What is the command to create a page file with 100,000 blocks and a swap file. I want to create it on a Vax 7630 Running openvms

Re: creating page and swap files

Ian Miller. — Wed, 03 May 2006 14:31:13 GMT

create a file
$ MCR SYSGEN CREATE dev:[dir]PAGEFILE.SYS/SIZE=100000

to extend the default file
MCR SYSGEN CREATE SYS$SYSTEM:PAGEFILE.SYS/SIZ=100000

install it as a pagefile

$ MCR SYSGEN INSTALL dev:[dir]PAGEFILE.SYS/PAGE

Remember to add the command to mount this device and install the page file into
SYS$MANAGER:SYPAGSWPFILES.COM

Re: creating page and swap files

vmsserbo — Wed, 03 May 2006 14:58:20 GMT

tHANKS

Re: creating page and swap files

comarow — Wed, 03 May 2006 18:31:27 GMT

Miles,

The sysgen will always work.
@sys$update:swapfiles will only expand your primary files.

I did want to point out something to folks
that are rarely able to reboot their systems. They prepare for emergencies
by incresing Pagefile_Count to a larger number than their current number of pagefiles. Thus if they run into a need to add yet another pagefile, they don't need to reboot.

Have fun,
Bob

Re: creating page and swap files

Ian Miller. — Thu, 04 May 2006 03:18:08 GMT

"Pagefile_Count" ?
Do you mean PAGFILCNT system parameter ?

No harm in setting it bigger than you need.

In recent versions this was obsoleted and the pageswap file vector is set to max size (254 files). Its only one longword per file so does not occupy significant non-paged pool.

Re: creating page and swap files

Karl Rohwedder — Thu, 04 May 2006 03:33:45 GMT

Beware when extending a pagefile, that SYSGEN seems to use a contigous-best-try algorithm, when allocating space. If your disk is fragmented, you may end up with a lot of little chunks. The problem is that the pagefile has no additional fileheaders.
So sometime I just check for the biggest free extent and add just this to the current size and so on.

regards Kalle

Re: creating page and swap files

Ian Miller. — Thu, 04 May 2006 06:10:04 GMT

Karl,
the SYSGEN CREATE command has quaifiers to specify that the created file is either to be contiguous (/CONTIGUOUS) or contiguous-best-try (/NOCONTIGUOUS). /NOCONTIGUOUS is the default.

Re: creating page and swap files

Karl Rohwedder — Thu, 04 May 2006 06:15:34 GMT

Ian,

that is right, but if if you don't have enough contigous space and use best-try, SYSGEN takes the 2 biggest chunks of free space and goes then down the list, even if there a bigger chunks lying around elsewhere on the disk.

regards Kalle

Re: creating page and swap files

comarow — Thu, 04 May 2006 09:22:50 GMT

On the topic of contiguous space, that is very critical.

What I've seen happen too many times is a customer runs autogen, perhaps even as a result of an upgrade. Based on feedback,
the system thinks you need a 500,000 block
pagefile.

The system has an existing 300,000 block pagefile. It tries to create it, but there's not enough reasonably contiguous space, so it creates a 50,000 block page file. Then the system hangs because of it.

Thus, to prevent this from happening, add
Pagefile=0, swapfile=0 in modparams.dat
and taking complete control over their sizing.

One strange thing to me... When you add memory, you generally will need less pagefile useage, but autogen will increase the size of the pagefile.

AGEN$FEEDBACK.DAT will have the peak useage of the pagefile saved, so you can look at that file. It is a simple ascii file.

Thanks for the correction on pagefile count.
I was planning on getting the exact name.

Re: creating page and swap files

Arch_Muthiah — Fri, 05 May 2006 16:31:46 GMT

Miles,

$ RUN SYS$SYSTEM:SYSGEN
SYSGEN> create disk:[sys0.sysexe]pagefile.sys/size=any_size

Pagefile guidelines:

PAGEFILE sizes are normally sufficient if the combined total size of all pagefiles equals double the amount of total physical memory. In addition, during peak times you should have at least 33% of each pagefile free. Having sufficiently large pagefiles greatly enhances system performance.

Archunan