[OpenAFS] What filesystem?

Rodney M Dyer rmdyer@uncc.edu
Sat, 04 Mar 2006 13:35:28 -0500

At 11:45 AM 3/4/2006, Christopher D. Clausen wrote:
>Actually, that is pretty much all it is.  Its a namespace for CIFS 
>shares.  The replicas work with the File Replication Service (frs) and can 
>operate even without a domain controller, although most places will want 
>the data hosted in active directory.  The file replication can be more 
>advanced than one to many replication.  Active Directory has a concept of 
>"sites" and this can be utilized to save data transmission time over WAN 
>links between branch offices.  Group Policy can be used to point different 
>sets of machines at different servers by default, failing over to other 
>sites when needed.

And for these reasons you can forget common name space ACLs, groups, and 
such unless you have a single AD where all your shares are from AD domain 
member servers and you are a member of the domain.  And since it is CIFS 
based, there's no concept of a local cache to reduce network traffic.  As 
well the Dfs root node must be authenticated to, meaning clients at home 
(or remote on the Internet) must be members of the AD domain that the root 
node belongs to.  And btw, who in their right mind would share out CIFS 
over the Internet these days?  A strict comparison of AFS to Dfs would look 
something like...

AFS:  Yes, Yes, Yes, Yes, Yes, Yes
Dfs:  No, No, Sometimes, Maybe, Unsure, Not documented, etc. etc...

About the only thing Dfs has going for it -are- the automatic replication 
facilities, which most people in the AFS world find rather odd.  You see, 
in the AFS world, most of the tree is in the form of read-only replicated 
sites.  Only the user volumes and a few others are read-write.  And when a 
read-write volume goes down, you really don't want to "fail-over".  The 
business of read-write volumes for critical data should be in the form of 
RAID, not fail-over volumes.

It's kind of hard to explain, but Windows people and Unix people think 
differently about what they are serving out.  AFS grew up in a world where 
Unix admins wanted to distribute executable "applications" as well as data 
from a single name space tree.  In the enterprise, Unix workstations 
actually run their applications off of the network.  Very few people using 
AFS actually install applications on their local workstations.  This makes 
application distribution to thousands of workstations into a single vos 
replicate command.  Try that with Windows!  Windows application 
installation and distribution is a royal pain in the ass for admins and is 
why Windows has such a high cost of ownership for the enterprise.  Ever try 
running applications off your Windows server Dfs tree?  For that matter, 
how many Windows applications have you come across that are actually made 
to install on the network?  AFS has the concept of the "dotted" cell path 
which gets you to the read-write tree of volumes.  At our site we release 
an application and test it using the "dotted" path before any of our real 
workstations see it in the "read-only" tree.  When it is tested and ready, 
we issue a vos release command, which updates all the read-only sites and 
makes the application available to all the workstations.  Through blood, 
sweat, and tears, we've rigged our Windows XP environment to work much like 
the way our Unix environment works and it has saved us a hell of a lot of 
admin time.

<on soapbox>My conspiracy theory is that in the Microsoft Windows world of 
the 90's, there was virtually no incentive for Microsoft to "help" vendors, 
or establish rigorous rules, methods, and policies for how applications can 
run off the network.  Applications run faster off of the local disk, and 
Microsoft had no intention of helping vendors like Novell with applications 
that can run off their network.  For sure, even Microsoft didn't want their 
Office suite of applications to "appear" to run slowly compared to the Unix 
world, where the apps typically were executed off of NFS shares.  It 
certainly was a big boon for hard drive makers since users keep needing 
bigger and bigger drives to store their applications on.  Remember how slow 
the network used to be?<off soapbox>

Windows admins on the other hand tend to put DATA, not applications, on the 
network.  Most Dfs trees lead only to user volumes and some shared database 
files, or common Office shares.  The auto-replication facilities of DFS 
would work fine in this circumstance.

We've setup a Dfs tree along side our AFS tree, but haven't used it much at 
all.  Our primary intention was to have something to go to if the OpenAFS 
Windows client turned out to be unsupported when Transarc was broken 
up.  Companies like Network Appliance sell NAS gear that can be used in Dfs 
environments too.  Now, the OpenAFS Windows client has great support 
through developers like Jeffrey Altman of Secure-Endpoints.

Frankly, Microsoft's support of Dfs so far has been abysmal.  They really 
don't promote it at all.  They see it as just something that some 
enterprises might be interested in doing.  And only those enterprises that 
can afford to get enterprise level support contracts get any real help.  In 
effect, Microsoft is using the enterprise for a test-bed of technologies 
like Dfs.  It's only when they actually get enough documentation and 
features into it that they start to promote it to the world.  I mean three 
years ago, you were lucky to find anything beyond some obscure white papers 
on Dfs.  Dfs does work, but in the real world when most Windows IT groups 
are interested in setting up big trees of data they actually end up turning 
to NAS or SAN.

Like you said, Dfs is primarily an all Windows technology anyway.  If you 
need anything heterogeneous then you must turn to AFS.


Rodney M. Dyer
Windows Systems Programmer
Mosaic Computing Group
William States Lee College of Engineering
University of North Carolina at Charlotte
Email: rmdyer@uncc.edu
Web: http://www.coe.uncc.edu/~rmdyer
Phone: (704)687-3518
Help Desk Line: (704)687-3150
FAX: (704)687-2352
Office:  Cameron Applied Research Center, Room 232