[Linux-cluster] page and buffer cache in Linux File Systems

[John Que]

Hello,

I am a newbie to Linux Clusters and to Clusters File Systems in
particular.

I am reading a book which was recently published, named: "Building Clustered
Linux Systems" By Robert Lucke.(Published by Prentice Hall PTR /HP 
Professional
Series.)
(http://www.phptr.com/title/0131448536)

I have a question regarding buffer or page cache on cluster file systems.

I saw in Chapter 14 (page 429), the follwing text
(in 14.4 Commercially Available Cluster section):

"There is a set of common requirements that you'll find in all parallel
file systems used in Linux Clusters...
For datatbas use,you will find that the file systems needs to provide some 
form
of direct access mode,in which the database software can read and write data
blocks without using the Linux System's buffer or page cache.
The database software performs this caching itself and removes the 
associated
overhead".

The author here talks about a subset of Linux Clusters File Systems,
(parallel file systems);Specifically he mentioned PVFS1 and PVFS2.

What I do not understand is this:
Is this requirment specific to Cluster File Systems?
Because as I understand, this same requirement should exist also
for ordinary (non clustered) file systems like ext3.

Does anybody know of a clustered file system which implements such 
requirement?
Is there a way to configure / setup a clustered file system to avoid
page/buffer cache ? (to enable what the author calls "direct access mode").

Any pointers to info on this are welcomed.

And , I am not an expert in ext3 , but:
in case such a requirement DOES exist for non clustered file systems
(like ext3) - does ext3 implement this requirement ? How?

Regards,
John

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