Linux RAID & XFS Question - Multiple levels of concurrency = faster I/O on md/RAID 5?

[John Robinson]

On 01/11/2008 12:00, Justin Piszcz wrote:
> On Sat, 1 Nov 2008, John Robinson wrote:
>> On 01/11/2008 08:29, Justin Piszcz wrote:
>> [...]
>>> Why is running 3 jobs con-currently that take care of two parts each 
>>> more than
>>> twice as fast than running one job for six parts?
>>
>> Because you have multiple CPUs?
> 
> So 1/4 of a quad core q6600 cannot achieve higher rates of I/O due to the
> parity operations being that costly?
> 
> Is the only way to increase the single-threaded speed to increase the 
> maximum
> CPU core speed/get a faster CPU, and/or theoretically a multi-threaded 
> md-raid
> could maximize throughput?

Actually I was thinking that your test job - I think you said it used 
tar - is single-threaded and CPU-bound on one core, and doesn't saturate 
the MD subsystem. Your jobs are 75% user time to 25% system time, and 
the user time is not parellelisable until you do it yourself by 
splitting the work up.

Cheers,

John.