Coda File System

Re: Is Coda Right For Me.

From: Kevin Atkinson <>
Date: Wed, 16 Oct 2002 00:09:24 -0400 (EDT)
On Tue, 15 Oct 2002, Jan Harkes wrote:

> > If coda does indeed have these limitations, are there any plans on 
> > addressing them?
> Not really, I like it the way it is :)
> [Cut explanation on complicates dealig with file fragaments will bring]

Instead of treating partly retrieve files as file fragments or blocks why
not simply treat them as that.  That is instead of insisting upon
retrieving the whole file simply retrieve the part requested and mark the
file as partly retrieve on the client and just the client.  The server
does not need to worry about which parts the client has, it only has to
worry that it has some parts thus simplifying things greatly.  When any
part of the file changes the the server can notify the client like it
currently does (if I understand how Coda works) and it is up to the client
to worry about updating its cache.  Of course there should be the option
to retrieve the whole file as that behavior is sometimes desirable.

If I understand it correctly the current behavior is that when a file is 
opened the open call will block until the entire file is in the cache.

With the new system the open call can return immanently.  Then in the 
background it can start to retrieve the file.  The amount of the readahead 
the is performed can be configured by an setting an option which ranges 
from 0 to 1 where 0 means only retrieve the parts of the file requested, 
and 1 means to retrieve the whole file.  Numbers in between will mean to 
read ahead some but don't retrieve the complete file imminently.

Just an idea.  I certainly don't have the time to implement it ;)

I see the fact that coda has to download the entire file at once before
any reads can take place as a rather serious limitation.  There are many
times when only the first part of of a file is read in and the user has no
intention of reading the rest of the file.  For example when scanning a
directory of JPEGS with previews or Music files for the tag information.  
Etc...  The larger the files are the more of an issue this becomes.

And when dealing with huge files 1+ Gig files it really matters.  I really
don't want to download the entire file just to preview the first couple of

I will have to think about this a while as I am not sure Coda would be the 
best solution.

Received on 2002-10-16 00:13:41