Dump devices and primary swap

[Jay_122]

Hi,
I created a primary dump lvol and added it using the lvlnboot -d command. I rebooted the server and see the new dump volume with lvlnboot -v and crashconf -v. Now that this is complete, I would like to remove primary swap (lvol2) from being a dump device.
My questions are 1) how do I do this? 2) Should I do this? I have disabled savecrash and want to make sure that no dump information is written to swap because it will not be saved.

All opinions are welcome.

Thanks,
Jay

[Marco A.]

You cannot remove 'lvol2' which is your primary swap.
Also, unless you have free, contiguous extents immediately adjacent to the last physical extent of 'lvol2' you cannot extend primary swap, /, primary swap and /stand must be contiguous and cannot be extended with lvextend.

Regards

[A. Clay Stephenson · Accepted solution]

You need to run lvrmboot -v -d lvol2 /dev/vg00. This will remove /dev/vg00/lvol2 as a dump device but leave any of its other functions (e.g. primary swap) intact.

[Sundar_7]

Jay,

l) use the lvrmboot command as suggested by Clay

2) Should you do this ? Yes, it is usually a good idea not to use the swap as the primary dump device. But if you need to understand why, here is my understanding.

When the system panics, the kernel is going to dump the memory to the primary dump device (i.e to lvol2 in this case) and reboot the system. Savecrash at bootup will dump the lvol2 to /var/adm/crash (default).

But if for somereason, savecrash could not save the crash dump, the system will continue to boot (if it can ,ofcourse). Now if your lvol2 is both the swap and the dump device, and if your system starts swapping, the dump contents will be overwritten and you can no longer be able to save them to the filesystem.

The dump is usually written starting from the bottom of the device, working backwards. So , depending on the size of your swap device and dump configuration, you could still be able to save the crash dump, even if you system is swapping,ofcourse only if your swap device is not 100% used.

Confusing enough ? :-) hope this helps.

Sundar

[A. Clay Stephenson]

Combining the function of swap and dump into one device has always been dumb -- these are entirely different functions and never the twain should meet. The default behavior (combined primary swap and dump) is an artifact of both the cost and the size of disks of only a few years ago. Now that "small" disks are only 36GiB (if you can find any that small), combining the areas makes no sense. For me, the main benefit of separating swap and dump is that valuable minutes during the reboot cycle are saved because there is no need to compress and save the dump image because it is still intact.

[Jay_122]

Clay / Sundar,
Thanks for all the information and advice, it's appreciated.

Br,
jay

[Jay_122]

Thanks for all the help!!