Re: recommendations for stripe/chunk size

[Bill Davidsen <davidsen@tmr.com>]

Wolfgang Denk wrote:
> In message <47AA08E7.5000801@tmr.com> you wrote:
>   
>>> I actually  think the kernel should operate with block sizes
>>> like this and not wth 4 kiB blocks. It is the readahead and the elevator
>>> algorithms that save us from randomly reading 4 kb a time.
>>>
>>>   
>>>       
>> Exactly, and nothing save a R-A-RW cycle if the write is a partial chunk.
>>     
>
> Indeed kernel page size is an important factor in such optimizations.
> But you have to keep in mind that this is mostly efficient for (very)
> large strictly sequential I/O operations only -  actual  file  system
> traffic may be *very* different.
>
>   
That was actually what I meant by page size, that of the file system 
rather than the memory, ie. the "block size" typically used for writes. 
Or multiples thereof, obviously.
> We implemented the option to select kernel page sizes of  4,  16,  64
> and  256  kB for some PowerPC systems (440SPe, to be precise). A nice
> graphics of the effect can be found here:
>
> https://www.amcc.com/MyAMCC/retrieveDocument/PowerPC/440SPe/RAIDinLinux_PB_0529a.pdf
>
>   
I started that online and pulled a download to print, very neat stuff. 
Thanks for the link.
> Best regards,
>
> Wolfgang Denk
>
>   


-- 
Bill Davidsen <davidsen@tmr.com>
  "Woe unto the statesman who makes war without a reason that will still
  be valid when the war is over..." Otto von Bismark