Subject: [nfsv4] Metadata striping

From: Peter Braam <[email-masked]>
Date: Wed, 19 Nov 2008 12:55:41 -0700

Pardon my ignorance of NFS and the intrusion.  When reading through the
metadata striping document (
http://tools.ietf.org/id/draft-eisler-nfsv4-pnfs-metastripe-01.txt ) the
following thoughts and questions came up.

The attributes of a file can be summarized as:

Its identifier as entered in directories, let¹s call this a fid
The core file attributes, such as owner, mode, pointers to extended
attributes
Further attributes, such as layout information
The data in the file

I think I understand how further attributes and data location can be
specified with a layout associated with the file.   When striping metadata
the first question that comes up is the layout of the core file attributes
(Lustre calls this the location of the FID).  If a file system/protocol has
a lookup function a natural step to take is to

1. do a lookup of the fid based on parent fid and name
2. get the location of the fid  i.e. the places where to find the core
attributes.

If the namespace is spread over multiple nodes, the result of ³2² is not
always the same node that held the directory.  Also, the location of the fid
can already contain striping information, e.g. having  replicas of the core
file attributes is  a good ting.  How does the proposal leverage this?  Here
is some speculation as to how this might work.

An operation such as NFS Open probably requires the core attributes, so I am
speculating that  open(parent_fh, name, ....) would be sent to an I-MDS node
holding the ³name² section of the parent_fh; then that I-MDS would get
attributes from a secondary L-MDS to complete the open RPC.   It seems that
only on subsequent operations the client would be able to contact the L-MDS
directly.  Are there RPCs that the I-MDS is making to obtain the layout of
the core attributes?

I wonder if I have missed something or if some clarification about the
striping of the core data is required.

Thank you.

Peter

_______________________________________________
nfsv4 mailing list
[email-masked]
https://www.ietf.org/mailman/listinfo/nfsv4