Re: Linux supports hot-swappable hardware? [was Re:

On Wed, 18 Jun 2003, Ernest E Vogelsinger wrote:

> At 14:41 18.06.2003, Shridhar Daithankar said:
> --------------------[snip]--------------------
> >
> >Linux supports hot-swappable hardware? As in swappng CPU/RAM/Add on cards on
> >the fly?
> >
> >That is news to me. Could you point me to more resources on this?
> --------------------[snip]--------------------
>
> AFAIK swappable hardware needs to be supported by the hardware as well.
> Currently hard disks and power supplies can be hot-swapped, I never heard
> of the possibility to hot-swap directly on the data bus (memory, CPU, slot
> cards).

Mainframes and Sun E class servers have supported this for years, with
their own OS in place. RUnning Linux in an LPAR on a mainframe allows you
to do this right now, albeit requiring the linux image to be restarted to
see the change.

There ARE kernel patches in the works for 2.5/2.6 to allow this, and
patches already released against older 2.4 kernels to allow it.

http://lwn.net/2001/0510/a/hot-swap-cpu.php3

Note I didn't say that linux works right for this yet, but that it's
coming.

> As for SCSI disks and Power supplies, Linux supports hot swap. Check out
> Dell servers for example.

Linux doesn't need to do anything to allow that, only the hardware needs
to. It's kept away from the kernel by the RAID controller (in the case of
disks) or just not noticed in the PS department.

I've got a Dual PPro-200 under my desk with hot swappable power supplies
and hot swappable hard drives that I build in 1997...

Intel hardware is still way behind Sun or IBM when it comes to hot
swapping memory and CPU, but at least it's catching up with swappable PCI
cards finally.

Remember, Linux != X86 hardware only.