Re: IDE hotplug support?

["Jakob Østergaard" <jakob@unthought.net>]

On Thu, May 02, 2002 at 08:19:04PM +0200, Martin Dalecki wrote:
...
> 15 drives == 16 interfaces == 8 channels == 4 controllers
> with primary and secondary channel.

Usually using both master and slave on an IDE channel spells disaster
performance wise, and I would be surprised if the hotplug stuff worked
with this as well...

> 
> He will have groups of about 4 drives on each channel wich
> serialize each other due to excessive IRQ line sharing and
> master slave issues.

Use 8 controllers for the 15 (16) drives.

> 
> 8 x 130MBy/s >>>> PCI bus throughput... I would rather recommend
> a classical RAID controller card for this kind of
> setup.

Because RAID controllers do not use the PCI bus ???    ;)

The bus-overhead on RAID-5 is not too bad unless you specifically construct
a workload to make it so (writes-only, scattered so that the kernel cannot
cache stripes to avoid read-in for parity calculation).

Sure, the PCI bus will be a bottleneck, and PCI overhead alone will decrease
the real-world performance to somewhere below the theoretical PCI bandwidth
limitations, but don't let this blind you  -  100 MB/sec sustained transfers
can still be "good enough" for many people.

By the way, has anyone tried such larger multi-controller setups, and tested
the bandwidth in configurations with multiple PCI busses on the board, versus a
single PCI bus ?

-- 
................................................................
:   jakob@unthought.net   : And I see the elder races,         :
:.........................: putrid forms of man                :
:   Jakob Østergaard      : See him rise and claim the earth,  :
:        OZ9ABN           : his downfall is at hand.           :
:.........................:............{Konkhra}...............: