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PDT on HP-UX 11.11

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Tom Wolf_3
Valued Contributor

PDT on HP-UX 11.11

Hello all.
I have a few questions concerning the Page Deallocation Table (PDT) on our rp7410 running HP-UX 11.11.

As in attachment, there are currently 20 entries in the PDT being used.

What happens when all 100 entries are used?

Is the DIMM responsible for the single bit errors deallocated at that point?

If additional pages need to be deallocated and the table is full, what happens?

Also, the DIMM generating the single bit errors is DIMM 0C in CAB/CELL 0/1.
If the errors become too numerous and the problematic DIMM is deallocated, is it just that particular DIMM or are all the DIMMâ s in that slot deallocated, which would be DIMMâ s 0A, 0B, 0C, and 0D in slot 0 of CAB/CELL 0/1.

Just looking for a bit of clarification.

Any links to HP doc's discussing this would be excellent.

Thanks in advance.
Acclaimed Contributor

Re: PDT on HP-UX 11.11

>> Logging interval: 480 seconds.

This indicates the system want to test the suspect area, but it can't because it is still in use.

Reboot the system to allow the test and watch it.

If an area is suspect, it will be tested and deallocated if not working (4k blocks on the dimm).

If it cannot be tested, even a single error will be reported again and again until it is tested.

Hope this helps!

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Honored Contributor

Re: PDT on HP-UX 11.11

PDT Summary (ignore the T-class resolution section):

PDT errors and risks:

As to what will happen it depends upon several things. It won't be able to run the self tests and will warrant memory replacement.

Older versions of STM didn't handle PDT correctly on some systems. Other systems have had system firmware updated to increase the PDT size to 256 or larger.

Patches have also been developed to address PDT issues.

If it fills up then system stability could become an issue and/or data loss may occur.

So make sure Patches, STM and Firmware is up to date. Replace suspect dimms and clear the PDT after replacement.


Honored Contributor

Re: PDT on HP-UX 11.11

To answer your questions:

>> If additional pages need to be deallocated and the table is full, what happens?

In short, nothing. When the PDT is full, no further pages are deallocated. The system continues to process single bit errors, but if any multi-bit errors occur on these pages, the system will crash.

>> If the errors become too numerous and the problematic DIMM is deallocated, is it just that particular DIMM or are all the DIMMs in that slot deallocated.

All four DIMMs within that bank would be deallocated.

Note, that the above applies to the rp7410/rp8400 and similar servers. Newer systems that employ "chip kill" or DRAM sparing, will perform differently in this situation. This is basically enhanced ECC protection that would allow for a DRAM chip to fail and allow the system to continue to run.

HP used to have a whitepaper on it, but I cant seem to find it.


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Re: PDT on HP-UX 11.11

you can clear the PDT in mstm when the OS is running. mstm--tool--utility---run---logtool--memory---clearlog, however just like the above master's  advise that clear the PDT after you replace the memory.