zfs discuss - Jan 2007 - A little different look at filesystems ... Just looking for ideas

Here''s something I''ve been noodling around for a while.
I''d like to run
this by some of you in this forum and see what you think. If I''m off
topic, I apologize.

ZFS gives large companies the ability to have huge amounts of data
available to the desktop user. Moving the user data from a locally
installed system to a ZFS based server makes a huge amount of sense, not
only saving money in the base configuration of the desktop, but also in
maintenance, and backups etc ... It make mobility within the company
easier, as they can just access the files from anywhere IN the company. 

That''s wonderful. Only there is one small problem. Many companies that
are having major issues with mobility are giving more and more employees
laptops. Some of the data they need can be gotten off the Company''s
portal, but it still requires the OS and applications to be installed
locally, and user data to be on the local disk as well. As more and more
laptops are purchased, the issues simply multiply, and the company now
has the same maintenance issues they started with!

What if something like the old CacheFS was revived, using ZFS as the
base file system instead of UFS? Using the ZFS filesystems on servers as
the "master" systems, the laptop builds a "cache" of files,
used in the
last month or so. Could be applications or user data, it would not
matter. If the system was disconnected from the network, say on an
airplane, the data and applications would still be available. Using the
Copy on Write method in ZFS, the local cache of user data would then
update when connected back to the server. If anything happens to the
system, the only files actually lost would be what was done since the
last update to the master. 

This model could be used at the desktop as well. It would effective
reduce the bandwidth needed for NFS mounted clients, and could handle
far many clients than without a cache. In the end, the only thing
different from a laptop and a desktop might be the size of the cache. If
there was a problem, simply clean the cache out and start over. This
also would commonize the maintenance models between laptop and desktop. 

Could this be a good thing, or am I way off base??? 


Gary A. Ross
Network Operations Architect
Ford Motor Company
gross at ford.com
Phone: (313) 390-4313

On Jan 26, 2007, at 10:57, Ross, Gary (G.A.) wrote:
> ...
> What if something like the old CacheFS was revived, using ZFS as the
> base file system instead of UFS?
>  ...
>
> Could this be a good thing, or am I way off base???
Disconnected operation is a hard problem.  One of the better research 
efforts in that area was CODA, at CMU.  CODA was, as I recall, and 
extension to AFS, but it''s probably reasonable to take some of those 
ideas and marry them with ZFS.  CODA is now open-source; at least the 
BSDs have it.

	--Ed

On Fri, Jan 26, 2007 at 11:11:13AM -0800, Ed Gould
wrote:
> 
> Disconnected operation is a hard problem.  One of the better research 
> efforts in that area was CODA, at CMU.  CODA was, as I recall, and 
> extension to AFS, but it''s probably reasonable to take some of
those
> ideas and marry them with ZFS.  CODA is now open-source; at least the 
> BSDs have it.
It''s funny you should mention CODA.  I''ve just recently
started looking at it
as a way to get davfs mounting support onto Solaris.

It''s not been easy.  The CODA Solaris kernel module is several years
old and
looks like it hasn''t been touched in at least 2 years.  It does not
cleanly
build on svn_50.  CODA itself has issues as well.

CODA certainly looks like an interesting option as it makes it very easy to
support filesystems under Solaris (we *still* lack smbfs for pete''s
sake)

It seems like lots of work is going to be required to make it useful however.

NetBSD 3.1 is currently getting installed on my Ghetto Laptop, at which point
I will start playing with CODA.  If I like what I see, I''ll probably
look into
spending some time trying to at least get the kernel module working.

-brian
-- 
"The reason I don''t use Gnome: every single other window manager I
know of is
very powerfully extensible, where you can switch actions to different mouse
buttons. Guess which one is not, because it might confuse the poor users?
Here''s a hint: it''s not the small and fast one."       
--Linus

Ross, Gary (G.A.) wrote:
> What if something like the old CacheFS was revived, using ZFS as the
> base file system instead of UFS? Using the ZFS filesystems on servers as
> the "master" systems, the laptop builds a "cache" of
files, used in the
> last month or so.
If we ignore the "merging" problem for a moment (ie, where the same 
file/s are changed on both server and laptop), then you can accomplish a 
lot of this today (albeit somewhat clunkily) using zfs send/recv.

Keep the "main" copy on the server, and use that when attached.  When 
the laptop wants to detach, just ''zfs send'' the latest changes
from the
server to the laptop.  If not too much has changed, this will be fast.

When the laptop reconnects, ''zfs send'' the changes back to the
server.

Essentially, you would want to change what is mounted on /home/$user 
based on where the "main" copy is stored.  When connected to the
server,
it should point to nfs://server/home/$user, but when disconnected, point 
to local_zpool/home/$user.  Connecting/disconnecting would involve doing 
the ''zfs send|zfs recv'' plus changing the mount.

The fs that is not currently the "main" one should be mounted
read-only
to avoid the merging problem.

As I said, this is clunkier than a "real" solution would be, but it 
makes for some interesting possibilities.

--matt