linux-kernel - Re: Pull request for FS-Cache, including NFS patches

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Date:	Fri, 19 Dec 2008 17:48:51 +0100
From:	Gabor Gombas <gombasg@...aki.hu>
To:	Trond Myklebust <trond.myklebust@....uio.no>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>,
	Christoph Hellwig <hch@...radead.org>, sfr@...b.auug.org.au,
	steved@...hat.com, rwheeler@...hat.com, bfields@...ldses.org,
	nfsv4@...ux-nfs.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: Pull request for FS-Cache, including NFS patches

On Fri, Dec 19, 2008 at 07:33:56AM -0500, Trond Myklebust wrote:

> One interesting use case that I didn't see David mention is for cluster
> boot up. In a lot of the HPC clustered set-ups there tend be a number of
> 'hot' files that all clients need to access at roughly the same time in
> the boot cycle. Pre-loading these files into the persistent cache before
> booting the cluster is one way to solve this problem. Server replication
> and/or copying the files to local storage on the clients are other
> solutions.

Not just boot up. Consider a room full of thin clients using nfsroot and
the lecturer saying "Now everybody open a browser" or "Now everybody
open Openoffice". With just NFS, it takes ages (there is a bottleneck of
a single gigabit link between the clients and the NFS server even though
the server itself has a 10gig card). If we redirect most of /usr/lib to
a small local flash with some LD_LIBRARY_PATH and bind mount trickery we
get an acceptable startup time. The flash is too small to hold even
/usr/lib (flash size: 500M, /usr/lib is: 927M) so it is not possible to
keep everything locally.

It would be really nice if the local caching could be handled
automatically and we would not need so many hacks, so I really look
forward trying FS-Cache if I have time. I used cachefs on Solaris ages
ago and I had good experiences back then; it would be really nice if
Linux would catch up.

Gabor

-- 
     ---------------------------------------------------------
     MTA SZTAKI Computer and Automation Research Institute
                Hungarian Academy of Sciences
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