9.8 Dump and Swap Space in the Same Volume

     

I mentioned at the beginning of this chapter that some people consider reserving dump space as a waste of space . I hope that we can see the value of ensuring that we capture a crashdump . The problem with dump space is that it is empty disk space that is waiting for an event that might never happen. Lots of administrators I know who have numerous dump devices will also use them as swap devices. This is a good idea because the more swap devices we have, the more swap space interleaving can take place, should we ever need to use swap space. If we were being especially careful, we could think about swap space first to establish how much swap space we want to achieve. We could then create multiple dump devices (remember, a dump device must be contiguous, but swap space doesn't need to be) that happened to match the requirements of our swap system. We can then configure our dump devices to be swap devices as well, simply by having a swap and a dump entry in the /etc/fstab file.

 

 root@hpeos003[]  cat /etc/fstab  ... /dev/vgora1/dump2       ...     dump    defaults 0 0 /dev/vx/dsk/ora1/dump3  ...     dump    defaults 0 0 /dev/vgora1/dump2       ...     swap    defaults 0 0 /dev/vx/dsk/ora1/dump3  ...     swap    defaults 0 0 root@hpeos003[] 

This makes good use of a device that will, we hope, never be used; while the system is up, we can swap to it, and when the system crashes, we can use it as a dump device.

If we have a device that is both a swap and dump device, we need to think about what happens if there is a crashdump to save and the swapping system wants to use the space. The default behavior for the savecrash utility is to allow swapping as soon as the crashdump has been saved (check the /etc/rc.config.d/savecrash file to configure alternative behavior). This means that using multiple swap/dump areas is a good idea because if there is an alternative swap device, it will be used while the crashdump is written to the /var/adm/crash/crash.X directory.



HP-UX CSE(c) Official Study Guide and Desk Reference
HP-UX CSE(c) Official Study Guide and Desk Reference
ISBN: N/A
EAN: N/A
Year: 2006
Pages: 434

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net