Subject: Re: [nfsv4] exporting with multiple pNFS layout types

From: "William A.(Andy) Adamson" <[email-masked]>
Date: Mon, 09 Jan 2006 09:37:40 -0500

> 
> >>>"William A.(Andy) Adamson" said:
>  > 
>  > 
>  > do we really expect a file system to be exported with multiple layout 
> types?
>       
>  > if so, how does a client choose which layout type to use?
>  > 
> 
> The client specifies the type in the "layout_type" parameter to LAYOUTGET
> As noted by others, the client can query available types from attributes.
> 
>      struct LAYOUTGET4args {
>              /* CURRENT_FH: file */
>              clientid4               clientid;
>              pnfs_layouttype4        layout_type;
>              pnfs_layoutiomode4      iomode;
>              offset4                 offset;
>              length4                 length;
>              length4                 minlength;
>              count4                  maxcount;
>      };
>  > 

this is how a client asks on the wire. my question is how does a client choose 
between multiple available layouts for a given file. e.g. what criteria do you 
have in mind that a client will use to choose between two valid and available 
layout types?

say a client can use either block or file layout to access a file, and that 
connectivity to all block/file data servers exists. which should a client 
choose and why?

i'm just trying to get some background on the use cases that drive the need 
for the added complexity of per file layout types.

-->Andy

>  > from draft-ietf-nfsv4-pnfs-00.txt:
>  > 
>  > 7.1  pnfs_layouttype4<> FS_LAYOUT_TYPES
>  > 
>  >    This attribute applies to a file system and indicates what layout
>  >    types are supported by the file system.  We expect this attribute to
>  >    be queried when a client encounters a new fsid.  This attribute is
>  >    used by the client to determine if it has applicable layout drivers.
>  > 
>  > 
>  > 7.2  pnfs_layouttype4<> FILE_LAYOUT_TYPES
>  > 
>  >    This attribute indicates the particular layout type(s) used for a
>  >    file.  This is for informational purposes only.  The client needs to
>  >    use the LAYOUTGET operation in order to get enough information (e.g.,
>  >    specific device information) in order to perform I/O.
>  > 
>  > 
>  > 
>  > 
>  > 
>  > 
>  > _______________________________________________
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>  > 
>  > 
> 
> --
> Brent Welch
> Software Architect, Panasas Inc
> Accelerating Time to Results(tm) with Clustered Storage
> 
> www.panasas.com
> [email-masked]
> 

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