SYSDUMP file size

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issinoho
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SYSDUMP file size

Post by issinoho » Mon Jul 08, 2024 5:16 am

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Hardware type: QEMU Standard PC (Q35 + ICH9, 2009)
Software type: OpenVMS x86_64 V9.2-2
Physical memory: 16253216 pagelets (7936 MB)
For this system running on a 16GB drive, how big would you expect the SYSDUMP file to be?

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Physical Name   Volume Name      Type   Err   Size     Free     Used   Cap
DKA0:           X86SYS           DKX0   0  16384mb   1245mb  15139mb    92%
Here is my current dump file, which is consuming nearly half the entire disk - is this as expected?

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SYSDUMP.DMP;1         7.75GB/7.75GB
What is the recommended approach to tuning this? Manual or Autogen?

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cct
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Re: SYSDUMP file size

Post by cct » Mon Jul 08, 2024 7:22 am

I extended my system disk to allow for some of this, but still used autogen to reduce the dump files to 4Gb:

Added to MODPARAMS.DAT:
MAX_DUMPFILE = 8388698 ! Maximum size for dump file space
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issinoho
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Re: SYSDUMP file size

Post by issinoho » Mon Jul 08, 2024 7:44 am

Thanks. Is there a formula for making sure the dump file is adequately sized?

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Re: SYSDUMP file size

Post by cct » Mon Jul 08, 2024 8:06 am

Take a look at the System Manager’s Manual, Volume 2: Tuning, Monitoring, and Complex Systems
Section 2.1 Understanding Dump Files
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Re: SYSDUMP file size

Post by reinhardtjh » Mon Jul 08, 2024 9:54 am

issinoho wrote:
Mon Jul 08, 2024 5:16 am

Code: Select all

Hardware type: QEMU Standard PC (Q35 + ICH9, 2009)
Software type: OpenVMS x86_64 V9.2-2
Physical memory: 16253216 pagelets (7936 MB)
For this system running on a 16GB drive, how big would you expect the SYSDUMP file to be?

Code: Select all

Physical Name   Volume Name      Type   Err   Size     Free     Used   Cap
DKA0:           X86SYS           DKX0   0  16384mb   1245mb  15139mb    92%
Here is my current dump file, which is consuming nearly half the entire disk - is this as expected?

Code: Select all

SYSDUMP.DMP;1         7.75GB/7.75GB
What is the recommended approach to tuning this? Manual or Autogen?
Just another data point. I have a V9.2-2 running on a 24GB system disk, 12GB (show memory shows 11.74GB) memory. The SYSDUMP.DMP file is 11.74GB. I've done a few other test installs that have been deleted and I'm pretty sure the install process sets a SYSDUMP.DMP to be the same size as your physical memory. I'm not sure what happens if your system disk is not big enough, I've always sized it generously above the memory size. From what I can tell OpenVMS takes about 3GB for code and such for the O/S.
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Re: SYSDUMP file size

Post by cct » Mon Jul 08, 2024 10:39 am

I always used to set DUMPSTYLE to 1 on AXP systems with limited system disk sizes, enabling Selective dump, hence a more suitable sized dump file. I haven't yet got around to playing with this on X86
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Re: SYSDUMP file size

Post by dgordon » Mon Jul 08, 2024 12:16 pm

DUMPSTYLE should be 128 on x86. (Recent versions. If HELP SYS_P DUMPSTYLE talks about interleaved dumps, it should be set to 128.) DUMPSTYLE is dynamic. Add it to MODPARAMS.DAT as well.

Dump off the system disk (DOSD) is much easier on x86 than previous architectures:
1) Add a disk to your VM, let's call it DKA100 in this example. Make it at least twice the size of memory.
2) INIT and Mount the disk.
3) Add the mount of DKA100 to your startup
4) SHOW LOGICAL SYS$TOPSYS. This will show you the root for the system. I'm presuming most x86 systems are SYS0 and that's what I'll use.
5) Create DKA100:[SYS0.SYSEXE] (or whatever TOPSYS is.)
6) $ MC SYSGEN CREATE DKA100:[SYS0.SYSEXE]SYSDUMP.DMP/SIZE=nnn where nnn is say 1/2 of the system memory size.
7) SET DUMP/DEVICE=DKA100:
8) SHOW DUMP
9) Rename the dump file on the system disk to something else. You can delete it now, but easier to delete once you've tested the setup.
10) Run AUTOGEN to re-size the dump file.
11) At some convenient time, test the dump file. From the console, hit ^P (that's control-P) twice and answer "y" to the crash question. Watch the dump happen.

Unlike previous architectures, the dump file is located at the time the dump kernel takes over.
Last edited by dgordon on Mon Jul 08, 2024 12:17 pm, edited 1 time in total.
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Re: SYSDUMP file size

Post by snadow » Mon Jul 08, 2024 1:35 pm

I'm casting another vote for DOSD (dump off system disk.) With everything virtualized these days, including disk storage, creating a LUN that just holds the dumpfile makes life a lot simpler, and frees-up space on the system disk. One of the best things that I ever did on a production AlphaServer that's still in use today: Anything (reasonably speaking) that doesn't need to be on the system disk, get it off of there!

As already mentioned, do test it though. It's never fun to have a crash, but it's even worse to discover that you didn't set up DOSD correctly and the dump didn't get written at all.

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Re: SYSDUMP file size

Post by arne_v » Mon Jul 08, 2024 3:05 pm

I would not install VMS x86-64 on a disk less than 30 GB. Nice to have a little wiggle room. Just my opinion of course.
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Re: SYSDUMP file size

Post by arne_v » Mon Jul 08, 2024 3:11 pm

If one has a support contract on the system or if one actually knows how to read a dump, then it makes sense to get as much data as possible in the dump file.

But if not then a dump file is not of much value.
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