Can I Mirror A Dump Area?

[Fred G. Claypool, Jr.]

Hello everyone,

I've read the 8/1/1997 post concerning this same topic (http://us-support.external.hp.com/cki/bin/doc.pl/sid=d650954b0029172f9a/screen=ckiDisplayDocument?docId=200000024628464), but since it's rather old, I wanted to confirm that this is still valid as of a new L-Class running HP-UX 11.00.

I assume most people mirror their swap areas (if they're using mirroring elsewhere) -- is this true?

Thanks,
~Fred Claypool, Jr.

[Patrick Wallek · Accepted solution]

Can you mirror a dump area? Sure. You can mirror ANY LV. The question is, why would you want to? Dump is the area that the memory will get written to when the machine goes through a TOC, panic, etc. I have my dump area the same as my swap area, so I do have it mirrored. If I had a different dump area, say another separate disk, then I probably wouldn't mirror it.

Yes I do mirror swap. If the disk that your swap lv is on crashes, you still want to be able to function. Primary swap is just another component of the root VG that should be mirrored. If you lose a root disk, and don't have swap mirrored, you could really be in trouble.

[Fred G. Claypool, Jr.]

Patrick,

Thanks for the quick response. You've answered my original question, but I've got a follow-up, just to satisfy my own curiosity.

In the event that the "dump" function really has to be called, and all of that data you mentioned gets written to my lvol, would I have any tools to read it, or would that be something only HP/Response or our HP engineers would use?

Thanks.

[Patrick Wallek]

Here's how the whole dump process works, at least as far as I know.

System panics, and memory is written to the dump area. On reboot the system looks to see if there is a dump data in the dump area, if so, it is then read from the dump area and written to /var/adm/crash. The files in /var/adm/crash are compressed. From there, there area things that you can do, I believe with the q4 utiltiy located in /usr/contrib/bin. If you know how to use that utility you can analyze the dump. I've used it once and that was with the guidance of an engineer from the Response Center.

[Thomas A. Martin]

Fred,

DocID OZBEKBRC00000611 explains how to use Q4 to prepare system dump files.

[Bill Hassell]

q4 indeed will prepare a readable set of lisitngs about the crash dump but you will need an HP-UX internals and dump reading class to make much sense out of it. q4 won't tell you that a patch is needed, only that something went wrong in a particular part of the kernel (like a corrupted table or pointer).

The Response Center can analyze the crash dump and compare the signatures with thousands of crash listings to determine a cause. In the worst case, the engineer would have to gather all the related source code plus any patch source code that applies and walk through the dump...a very labor intensive task.