From: Jake Gold <jake@dtiserv2.com>
Subject: Re: NFSv4 and client caching to local disk?
Date: Mon, 31 Mar 2003 10:38:50 -0800
Sender: nfs-admin@lists.sourceforge.net
Message-ID: <20030331103850.1f40a7f9.jake@dtiserv2.com>
References: <6440EA1A6AA1D5118C6900902745938E07D55473@black.eng.netapp.com>
	<3E8835A3.D5E64144@moving-picture.com>
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Cc: Charles.Lever@netapp.com, nfs@lists.sourceforge.net
To: James Pearson <james-p@moving-picture.com>
In-Reply-To: <3E8835A3.D5E64144@moving-picture.com>
Errors-To: nfs-admin@lists.sourceforge.net

I am also extremely interested in something like this.

I think the Zeus web server's model for in-memory caching would be great for NFS clients doing disk caching.

Something like this would be great:

cache_directory = /cache
	Directory where cache files are stored
cache_files
	Size of the web server file cache (number of files)
cache_small_file
	Maximum size of a 'small' file (bytes) (system page size)
cache_large_file
	Minimum size of a 'large' file (bytes)
cache_stat_expire
	Time for which the response of a stat() call is cached (seconds)
cache_max_bytes
	Maximum size to reserve for cached files (bytes) (0 = no limit)
cache_flush_interval
	Time after which unaccessed files are flushed from the cache (seconds)
cache_cooling_time Integer
	any file modified in the last 'n' seconds is not cached
cache_max_filename_length Integer
	filenames greater than this length aren't cached (Zero is no limit) 


I have a FAS940 with a cluster of Linux machines mounting _read-only_ volumes over NFSv3.
My situation is the same as James Pearson's....those machines read large, rarely modified files, where memory caching doesn't help a whole lot. It would be very nice to be able to have my under-worked local disks take some of the load off the filer.

Are there currently _any_ client-side NFS caching solutions (even something that requires some extra work)?

Thanks in advance,
Jake

On Mon, 31 Mar 2003 13:33:39 +0100
James Pearson <james-p@moving-picture.com> wrote:

> "Lever, Charles" wrote:
> > 
> > hi james-
> > 
> > > I'm trying to find out more about 'cachefs' type file systems
> > > that can
> > > cache NFS data to a client's local disk - I've come across a
> > > couple of
> > > references that seem to indicate that this may be possible with NFSv4.
> > >
> > > Does (will?) the Linux NFSv4 client support this feature?
> > 
> > Sun implemented cachefs on Solaris for earlier versions of NFS.
> > it really has nothing to do with which version of NFS that is
> > in use.
> 
> I've briefly looked at this on IRIX clients some time ago - but we don't
> have many IRIX boxes in use now.
>  
> > there is sporadic interest in a cachefs on Linux, and i know of
> > at least one generic prototype.  a specific implementation of
> > client-side disk caching that is available today is contained
> > in the Linux OpenAFS client (known as the AFS cache manager).
> 
> I have done some limited searching of the net for info and come across a
> few attempts with earlier kernels - and I am aware of some the
> issues/problems associated with doing this.
>  
> > cachefs becomes rather more interesting when used in conjunction
> > with NFSv4 file delegations -- that makes NFS behave in a fashion
> > similar to AFS client-side disk caching with callbacks.
> 
> My hopes were raised as the NFSv4 specs suggest that low level support
> for client disk caches is available - rather than being a 'bolt-on' for
> earlier versions - hence my question.
>  
> > there currently is no explicit plan to implement cachefs by the
> > team that is working on NFSv4 for Linux.  a disk cache has
> > rather limited usefulness compared to a memory cache.  what is
> > your application for it?
> 
> Mainly for reading large files that don't change (much) - i.e.
> effectively in a read-only mode. The total size of the required files is
> greater than the clients memory size - in fact any disk caching of NFS
> data doesn't necessarily need to survive a reboot of the client, so
> caching NFS file system data to swap could be enough for my needs ...
> 
> James Pearson
> 
> 
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