[Pvfs2-users] Number of data transfer messages

[Wantao]

Hi Michael,

Your reply helps me a lot. From the source code, I see that a flow has 8 buffers, and each buffer is 256KB. Does that mean each flow can transfer at most 8 messages, each message is 256KB? If that is true, what happens to a file larger than 2MB(8*256KB)? 

Thanks,
Wantao
 
 
------------------ Original ------------------
From:  "Michael Moore"<mtmoore at omnibond.com>;
Date:  Wed, Jun 29, 2011 08:06 PM
To:  "Wantao"<liu_wantao at qq.com>; 
Cc:  "pvfs2-users"<pvfs2-users at beowulf-underground.org>; 
Subject:  Re: [Pvfs2-users] Number of data transfer messages

 
 Hi Wantao,

In the situation you describe a single request will be sent to each server for your application's I/O request. When accessing a file the client needs to know what datafile handles are associated with the file, done via a getattr request, after that the client can perform I/O without contacting the metadata server. However, if the client updates attributes (atime, mtime, etc) as typically happens when using the kernel client interface, there will be a setattr request to the metadata server.
 
Hope that helps,
Michael 

On Wed, Jun 29, 2011 at 3:20 AM, Wantao <liu_wantao at qq.com> wrote:
 Hi, all

I have a PVFS2 installation with three IO servers and 64KB strip size. my application requests 256KB in one IO operation(read or write). So, it needs two continuous strips from server1 and one strip from server 2 and 3. In this case, how many data transfer messages are needed for server1? Can it send or receive two strips in one message?  Another question is that when accessing a big file, does PVFS2 need to interact with meta server for each IO operation? 
 
Thanks for all advice.

Wantao



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