what's difference hot plug with on line add & replace ?

[Hasell Blad]

Hi.

What is the difference 'Hot Plug' with
'On Line Add & Replacement' ?

[Michael Tully]

Hi,

In the past the term 'hot pluggable' meant you
could change components with a system outage.
These generally referred only disks, tape
drives and CD ROMS.
The 'OLAR' means that other components which
before needed an outage do not. For example
you can add a fibre channel card to a system
using the 'rad' command that will power down
a single slot, replace the component and
power on that slot again. The advantage of
this is, that a component has been added with
the aid of any outage. You could then plug this
card into a switch and enable some disks.

[Michael Tully]

Also have a look here for some additional info

http://devresource.hp.com/STK/impacts/i702.html

[S.K. Chan]

This is the definition of OLAR (from HP Technical DB)

Online addition and replacement (OLAR) is an HP-UX software feature that provides capability for replacing and adding PCI I/O cards to a system while the system is running, eliminating the need to reboot the system. OLAR was first introduced in HP-UX 11.0, and in HP-UX 11i is supported for L-class, N-class and Superdome-class systems.

Hot Plug means that a part can be changed with power applied and no damage to either the part or product will occur.

[Bill Hassell]

And it's really important to understand that replacing things like disks and I/O cards can have a very significant impact on the operating system. Some HP servers have hot-swap or hot-plug disks but unless the disk is properly removed from HP-UX, a system crash can be the result of changing a disk online. The hot-plug caspability only applies to the hardware, not the opsystem. Only disks in a disk array (where the array controller isolates real disks from the computer) can be swapped on a live system (within restrictions).