[Lustre-devel] read ahead

Oleg Drokin Oleg.Drokin at Sun.COM
Tue Dec 11 10:43:42 PST 2007


On Dec 11, 2007, at 1:25 PM, Peter Braam wrote:

> Can anyone tell me if read ahead in Lustre includes "early return"  
> features.  I mean that if I read 4K and readahead decides to fetch  
> 1M will my request get serviced when the first 4K arrives?  Is this  
> important?

I think this is impossible to implement with current architecture.
We have one bulk RPC (1M in size) that until received completely,  
won't issue any callbacks.
So only when that entire 1M is received your 4k request would return.
On the other hand if your example is 4k and 2M, then we will return  
after 1M that contains requested 4k is received (but there is no  
guarantee at the moment we won't receive second 2M first, I believe).


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