Re: IDE hotplug support?

[Samuel Flory <sflory@rackable.com>]

  Why not just grab a pair of 8 port 3ware cards?  Run raid 5 on each 
card, and throw 0 or linear via the md driver on top?

Jakob Østergaard wrote:

>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 ?
>
>  
>