[Lustre-discuss] File joining mechanism

[Nicolas Williams]

On Wed, Jan 13, 2010 at 10:23:06PM +0700, Lex wrote:
> I have some questions about file joining mechanism in lustre, so i post here
> and hope you can help me to clarify it :)
> 
> As we know, lustre use the split writing and hierarchy striping to
> distribute file object ( subfile)  to many osts in the cluster. When a
> client request one file ( over mds metadata ), these objects are retrieve
> from each ost to client.
> 
> So, the question is: when and where these objects are joined together to
> become a real file ?
> 
> Just guess, are there joined together in OSSs? If it's true, how these OSSs
> connect together to join its objects together? ( For example, assuming we
> have 2 OSSs, each OSS have 1 OST, file are striped across to 2 these OSTs.
> When a client request a file, i get to object in 2 different OST from 2
> different OSSs, so how these objects can combined together? )

On the client.

The MDS knows the layout of each file: the number and location of the
file's stripes.

The client obtains the layout from the MDS.

The client does I/O against the stripes of a file by talking directly to
the relevant OSTs.

Nico
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